Allow plugin to bypass any alias for grep.

This is an opt-in configuration.

doc/gitgutter.txt

@@ -95,6 +95,7 @@ You can customise:
 - The signs' colours and symbols
 - Line highlights
 - Extra arguments for git-diff
+- Whether or not to escape grep (defaults to no)
 - Whether or not vim-gitgutter is on initially (defaults to on)
 - Whether or not signs are shown (defaults to yes)
 - Whether or not line highlighting is on initially (defaults to off)
@@ -181,6 +182,13 @@ To pass extra arguments to git-diff, add this to your |vimrc|:
   let g:gitgutter_diff_args = '-w'
 <
 
+TO ESCAPE GREP
+
+To avoid any alias you have for grep, use this:
+>
+  let g:gitgutter_escape_grep = 1
+<
+
 TO TURN OFF VIM-GITGUTTER BY DEFAULT
 
 Add to your |vimrc|