[RFC] vim-patch:7.4.423

```
Problem:    expand("$shell") does not work as documented.
Solution:   Do not escape the $ when expanding environment variables.

https://code.google.com/p/vim/source/detail?r=v7-4-423
```

Original patch:
```diff
diff --git a/src/nvim/misc1.c b/src/nvim/misc1.c
--- a/src/nvim/misc1.c
+++ b/src/nvim/misc1.c
@@ -78,7 +78,8 @@ get_indent_str(ptr, ts, list)
 	    if (!list || lcs_tab1)    /* count a tab for what it is worth */
 		count += ts - (count % ts);
 	    else
-	/* in list mode, when tab is not set, count screen char width for Tab: ^I */
+		/* In list mode, when tab is not set, count screen char width
+		 * for Tab, displays: ^I */
 		count += ptr2cells(ptr);
 	}
 	else if (*ptr == ' ')
@@ -10767,7 +10768,7 @@ gen_expand_wildcards(num_pat, pat, num_f
 		    vim_free(p);
 		    ga_clear_strings(&ga);
 		    i = mch_expand_wildcards(num_pat, pat, num_file, file,
-								       flags);
+							 flags|EW_KEEPDOLLAR);
 		    recursive = FALSE;
 		    return i;
 		}
diff --git a/src/nvim/os_unix.c b/src/nvim/os_unix.c
--- a/src/nvim/os_unix.c
+++ b/src/nvim/os_unix.c
@@ -5939,10 +5939,12 @@ mch_expand_wildcards(num_pat, pat, num_f
 			*p++ = '\\';
 		    ++j;
 		}
-		else if (!intick && vim_strchr(SHELL_SPECIAL,
-							   pat[i][j]) != NULL)
+		else if (!intick
+			 && ((flags & EW_KEEPDOLLAR) == 0 || pat[i][j] != '$')
+			      && vim_strchr(SHELL_SPECIAL, pat[i][j]) != NULL)
 		    /* Put a backslash before a special character, but not
-		     * when inside ``. */
+		     * when inside ``. And not for $var when EW_KEEPDOLLAR is
+		     * set. */
 		    *p++ = '\\';
 
 		/* Copy one character. */
diff --git a/src/nvim/version.c b/src/nvim/version.c
--- a/src/nvim/version.c
+++ b/src/nvim/version.c
@@ -742,6 +742,8 @@ static char *(features[]) =
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    423,
+/**/
     422,
 /**/
     421,
diff --git a/src/nvim/vim.h b/src/nvim/vim.h
--- a/src/nvim/vim.h
+++ b/src/nvim/vim.h
@@ -835,6 +835,7 @@ extern char *(*dyn_libintl_textdomain)(c
 #define EW_ICASE	0x100	/* ignore case */
 #define EW_NOERROR	0x200	/* no error for bad regexp */
 #define EW_NOTWILD	0x400	/* add match with literal name if exists */
+#define EW_KEEPDOLLAR	0x800	/* do not escape $, $var is expanded */
 /* Note: mostly EW_NOTFOUND and EW_SILENT are mutually exclusive: EW_NOTFOUND
  * is used when executing commands and EW_SILENT for interactive expanding. */
```