Ignore escaped characters in date_format_order().

The PHP date-documentation says:

You can prevent a recognized character in the format string from being expanded by escaping it with a preceding backslash.

date_format_order() does not ignore these escaped characters which may results in an incorrect result.

FYI: My format example (which is actually just "j M"):

\<\s\p\a\n\ \c\l\a\s\s\=\"\d\a\y\"\>j\<\/\s\p\a\n\> \<\s\p\a\n\ \c\l\a\s\s\=\"\m\o\n\t\h\"\>M\<\/\s\p\a\n\>