(bug 36991) Fix jquery.tablesorter date sorting

(bug 36991) Fix jquery.tablesorter date sorting

jquery.tablesorter should extract date sort format from date string
instead of global config. Dates like "April 1 2012" and "1 April 2012" now sort correctly regardless of the content language's
DefaultDateFormat setting (exposed as wgDefaultDateFormat in
mw.config).

Previously jquery.tablesorter sorted dates like "1 Apr 2012" (DMY) or
"Apr 1 2012" (MDY) incorrectly. It just converted it to "1 4 2012"
and "4 1 2012", respectively, and then assumes MDY or DMY order based
on the global wiki configuration.

This patch fixes that.

Change-Id: I8061b1a7892633e34be4d4a0273a4dd5045fd2ee