Ensure order of files to open is not affected by 'suffixes'

Opening the same set of files in a new window and in an already open
window could result in the order of the files being different due to a
non-empty 'suffixes' option.  This patch clears 'suffix' before opening
multiple files and restores it afterwards.

src/MacVim/MMBackend.m

@@ -2376,6 +2376,10 @@ static NSString *MMSymlinkWarningString =
                     [cmd appendString:file];
                 }
 
+                // Temporarily clear 'suffixes' so that the files are opened in
+                // the same order as they appear in the "filenames" array.
+                [self addInput:@":let t:mvim_oldsu=&su|set su=<CR>"];
+
                 [self addInput:cmd];
 
                 // Split the view into multiple windows if requested.
@@ -2384,6 +2388,9 @@ static NSString *MMSymlinkWarningString =
                 else if (WIN_VER == layout)
                     [self addInput:@"|vert sall"];
 
+                // Restore the old value of 'suffixes'.
+                [self addInput:@"|let &su=t:mvim_oldsu|unlet t:mvim_oldsu"];
+
                 // Adding "|redr|f" ensures a "Hit ENTER" prompt is not shown.
                 [self addInput:@"|redr|f<CR>"];
             } else {