Make robust the replacement of temp file paths with actual paths.

The previous implementation meant the temp file paths were treated as
regular expressions, which was vulnerable to problems with backslashes
etc.

See #494.

test/test

@@ -2,6 +2,8 @@
 
 VIM="/Applications/MacVim.app/Contents/MacOS/Vim -v"
 
+export TEST=1
+
 $VIM -u NONE -U NONE -N                      \
   --cmd 'set rtp+=../'                       \
   --cmd 'let g:gitgutter_async=0'            \

test/test_gitgutter.vim

@@ -494,3 +494,72 @@ function Test_user_autocmd()
   call s:trigger_gitgutter()
   call assert_equal(bufnr, s:autocmd_user)
 endfunction
+
+
+function Test_fix_file_references()
+  " No special characters
+  let hunk_diff = join([
+        \ 'diff --git a/fixture.txt b/fixture.txt',
+        \ 'index f5c6aff..3fbde56 100644',
+        \ '--- a/fixture.txt',
+        \ '+++ b/fixture.txt',
+        \ '@@ -2,0 +3,1 @@ b',
+        \ '+x'
+        \ ], "\n")."\n"
+  let filepath = 'blah.txt'
+
+  let expected = join([
+        \ 'diff --git a/blah.txt b/blah.txt',
+        \ 'index f5c6aff..3fbde56 100644',
+        \ '--- a/blah.txt',
+        \ '+++ b/blah.txt',
+        \ '@@ -2,0 +3,1 @@ b',
+        \ '+x'
+        \ ], "\n")."\n"
+
+  call assert_equal(expected, gitgutter#hunk#fix_file_references(filepath, hunk_diff))
+
+  " diff.mnemonicPrefix; spaces in filename
+  let hunk_diff = join([
+        \ 'diff --git i/x/cat dog w/x/cat dog',
+        \ 'index f5c6aff..3fbde56 100644',
+        \ '--- i/x/cat dog',
+        \ '+++ w/x/cat dog',
+        \ '@@ -2,0 +3,1 @@ b',
+        \ '+x'
+        \ ], "\n")."\n"
+  let filepath = 'blah.txt'
+
+  let expected = join([
+        \ 'diff --git i/blah.txt w/blah.txt',
+        \ 'index f5c6aff..3fbde56 100644',
+        \ '--- i/blah.txt',
+        \ '+++ w/blah.txt',
+        \ '@@ -2,0 +3,1 @@ b',
+        \ '+x'
+        \ ], "\n")."\n"
+
+  call assert_equal(expected, gitgutter#hunk#fix_file_references(filepath, hunk_diff))
+
+  " Backslashes in filename; quotation marks
+  let hunk_diff = join([
+        \ 'diff --git "a/C:\\Users\\FOO~1.PAR\\AppData\\Local\\Temp\\nvimJcmSv9\\11.1.vim" "b/C:\\Users\\FOO~1.PAR\\AppData\\Local\\Temp\\nvimJcmSv9\\12.1.vim"',
+        \ 'index f42aeb0..4930403 100644',
+        \ '--- "a/C:\\Users\\FOO~1.PAR\\AppData\\Local\\Temp\\nvimJcmSv9\\11.1.vim"',
+        \ '+++ "b/C:\\Users\\FOO~1.PAR\\AppData\\Local\\Temp\\nvimJcmSv9\\12.1.vim"',
+        \ '@@ -172,0 +173 @@ stuff',
+        \ '+x'
+        \ ], "\n")."\n"
+  let filepath = 'init.vim'
+
+  let expected = join([
+        \ 'diff --git "a/init.vim" "b/init.vim"',
+        \ 'index f42aeb0..4930403 100644',
+        \ '--- "a/init.vim"',
+        \ '+++ "b/init.vim"',
+        \ '@@ -172,0 +173 @@ stuff',
+        \ '+x'
+        \ ], "\n")."\n"
+
+  call assert_equal(expected, gitgutter#hunk#fix_file_references(filepath, hunk_diff))
+endfunction