Add a trailing "/" to dirs in dialog autocomplete

The autocomplete feature in the "Run" dialog now adds a trailing "/"
when autocompleting directory names. This does three things:

1) shows you that you are completing a directory and not a filename,
2) saves one character of typing, and
3) makes it behave more consistent with shell (bash) autocompletion

src/dialog.c

@@ -263,6 +263,8 @@ ScanFiles(const char *dir, const char *prefix, unsigned acceptmask, unsigned dec
 				    WMFindInArray(result, (WMMatchDataProc *) strmatch,
 						  de->d_name + prefixlen) == WANotFound) {
 					suffix = wstrdup(de->d_name + prefixlen);
+					if (sb.st_mode & S_IFDIR)
+						wstrappend(suffix,"/");
 					WMAddToArray(result, suffix);
 				}
 				wfree(fullfilename);