Move current_branch() from git plugin to core lib/git.zsh

Fixes #4085: core -> plugin dependency issue.
Rename it to git_current_branch for clarity that it's git-specific.
Update all plugins that were calling it to use new name.
Fix variable leaks by making more variables in lib/git.zsh local.
Have lib/git.zsh use [[ ]] instead of [ ] everywhere.

themes/eastwood.zsh-theme

@@ -14,9 +14,9 @@ ZSH_THEME_GIT_PROMPT_CLEAN=""
 
 # Customized git status, oh-my-zsh currently does not allow render dirty status before branch
 git_custom_status() {
-  local cb=$(current_branch)
+  local cb=$(git_current_branch)
   if [ -n "$cb" ]; then
-    echo "$(parse_git_dirty)$ZSH_THEME_GIT_PROMPT_PREFIX$(current_branch)$ZSH_THEME_GIT_PROMPT_SUFFIX"
+    echo "$(parse_git_dirty)$ZSH_THEME_GIT_PROMPT_PREFIX$(git_current_branch)$ZSH_THEME_GIT_PROMPT_SUFFIX"
   fi
 }
 

themes/gallois.zsh-theme

@@ -1,3 +1,5 @@
+# Depends on the git plugin for work_in_progress()
+
 ZSH_THEME_GIT_PROMPT_PREFIX="%{$reset_color%}%{$fg[green]%}["
 ZSH_THEME_GIT_PROMPT_SUFFIX="]%{$reset_color%}"
 ZSH_THEME_GIT_PROMPT_DIRTY="%{$fg[red]%}*%{$reset_color%}"
@@ -5,9 +7,9 @@ ZSH_THEME_GIT_PROMPT_CLEAN=""
 
 #Customized git status, oh-my-zsh currently does not allow render dirty status before branch
 git_custom_status() {
-  local cb=$(current_branch)
+  local cb=$(git_current_branch)
   if [ -n "$cb" ]; then
-    echo "$(parse_git_dirty)%{$fg_bold[yellow]%}$(work_in_progress)%{$reset_color%}$ZSH_THEME_GIT_PROMPT_PREFIX$(current_branch)$ZSH_THEME_GIT_PROMPT_SUFFIX"
+    echo "$(parse_git_dirty)%{$fg_bold[yellow]%}$(work_in_progress)%{$reset_color%}$ZSH_THEME_GIT_PROMPT_PREFIX$(git_current_branch)$ZSH_THEME_GIT_PROMPT_SUFFIX"
   fi
 }
 

themes/josh.zsh-theme

@@ -9,7 +9,7 @@ function josh_prompt {
   (( spare_width = ${COLUMNS} ))
   prompt=" "
 
-  branch=$(current_branch)
+  branch=$(git_current_branch)
   ruby_version=$(rvm_prompt_info || rbenv_prompt_info)
   path_size=${#PWD}
   branch_size=${#branch}
@@ -31,7 +31,7 @@ function josh_prompt {
     prompt=" $prompt"
   done
   
-  prompt="%{%F{green}%}$PWD$prompt%{%F{red}%}$(rvm_prompt_info || rbenv_prompt_info)%{$reset_color%} $(current_branch)"
+  prompt="%{%F{green}%}$PWD$prompt%{%F{red}%}$(rvm_prompt_info || rbenv_prompt_info)%{$reset_color%} $(git_current_branch)"
   
   echo $prompt
 }

themes/juanghurtado.zsh-theme

@@ -1,5 +1,3 @@
-# Needs Git plugin for current_branch method
-
 # Color shortcuts
 RED=$fg[red]
 YELLOW=$fg[yellow]
@@ -40,4 +38,4 @@ ZSH_THEME_GIT_PROMPT_SHA_AFTER="%{$WHITE%}]"
 PROMPT='
 %{$GREEN_BOLD%}%n@%m%{$WHITE%}:%{$YELLOW%}%~%u$(parse_git_dirty)$(git_prompt_ahead)%{$RESET_COLOR%}
 %{$BLUE%}>%{$RESET_COLOR%} '
-RPROMPT='%{$GREEN_BOLD%}$(current_branch)$(git_prompt_short_sha)$(git_prompt_status)%{$RESET_COLOR%}'
+RPROMPT='%{$GREEN_BOLD%}$(git_current_branch)$(git_prompt_short_sha)$(git_prompt_status)%{$RESET_COLOR%}'

themes/mortalscumbag.zsh-theme

@@ -5,7 +5,7 @@ function my_git_prompt() {
   STATUS=""
 
   # is branch ahead?
-  if $(echo "$(git log origin/$(current_branch)..HEAD 2> /dev/null)" | grep '^commit' &> /dev/null); then
+  if $(echo "$(git log origin/$(git_current_branch)..HEAD 2> /dev/null)" | grep '^commit' &> /dev/null); then
     STATUS="$STATUS$ZSH_THEME_GIT_PROMPT_AHEAD"
   fi
 
@@ -37,7 +37,7 @@ function my_git_prompt() {
 }
 
 function my_current_branch() {
-  echo $(current_branch || echo "(no branch)")
+  echo $(git_current_branch || echo "(no branch)")
 }
 
 function ssh_connection() {

themes/peepcode.zsh-theme

@@ -28,7 +28,7 @@ git_dirty() {
 }
 
 git_prompt() {
-  local cb=$(current_branch)
+  local cb=$(git_current_branch)
   if [ -n "$cb" ]; then
     local repo_path=$(git_repo_path)
     echo " %{$fg_bold[grey]%}$cb %{$fg[white]%}$(git_commit_id)%{$reset_color%}$(git_mode)$(git_dirty)"

themes/sunrise.zsh-theme

@@ -1,6 +1,5 @@
 # Sunrise theme for oh-my-zsh
 # Intended to be used with Solarized: http://ethanschoonover.com/solarized
-# (Needs Git plugin for current_branch method)
 
 # Color shortcuts
 R=$fg_no_bold[red]