docs: Escape some backslashes for markdown

These no longer showed up correctly in the documentation.

https://bugzilla.gnome.org/show_bug.cgi?id=727346

glib/gfileutils.c

@@ -2114,7 +2114,7 @@ g_file_read_link (const gchar  *filename,
  * an absolute file name one that either begins with a directory
  * separator such as "\Users\tml" or begins with the root on a drive,
  * for example "C:\Windows". The first case also includes UNC paths
- * such as "\\myserver\docs\foo". In all cases, either slashes or
+ * such as "\\\\myserver\docs\foo". In all cases, either slashes or
  * backslashes are accepted.
  *
  * Note that a file name relative to the current drive root does not

glib/gkeyfile.c

@@ -119,7 +119,7 @@
  * are optional.
  * Space before and after the '=' character are ignored. Newline, tab,
  * carriage return and backslash characters in value are escaped as \n,
- * \t, \r, and \\, respectively. To preserve leading spaces in values,
+ * \t, \r, and \\\\, respectively. To preserve leading spaces in values,
  * these can also be escaped as \s.
  *
  * Key files can store strings (possibly with localized variants), integers,

glib/gregex.c

@@ -2765,7 +2765,7 @@ interpolation_list_needs_match (GList *list)
  * to the captured subexpression with the given name. '\0' refers
  * to the complete match, but '\0' followed by a number is the octal
  * representation of a character. To include a literal '\' in the
- * replacement, write '\\'.
+ * replacement, write '\\\\'.
  *
  * There are also escapes that changes the case of the following text:
  *