MDL-35469 fix Gecko based browser checks

The problem is that latest firefox versions stopped using dates because they lost the meaning over the time.
Automatically generated installer lang files
Automatically generated installer lang files
Automatically generated installer lang files
Automatically generated installer lang files
weekly release 2.1.8+
MDL-25948 upgrade: Fixing issues with upgrade from < 1.7 to 2.x.
Merge branch 'w42_MDL-35469_m21_geckover' of git://github.com/skodak/moodle into MOODLE_21_STABLE
MDL-36346 - YUI2 SWF vulnerability
Merge branch 'MDL-36346_21' of git://github.com/pauln/moodle into MOODLE_21_STABLE
Backport MDL-29872 to 21_STABLE
Automatically generated installer lang files
MDL-36346 - YUI2 SWF vulnerability, part 2
Merge branch 'MDL-36346_21' of git://github.com/pauln/moodle into MOODLE_21_STABLE
MDL-35558 mod_data: Show only own entries while there are required pending.
MDL-33791 Portfolio: Fixed security issue with passing file paths.
Merge branch 'install_21_STABLE' of git://git.moodle.cz/moodle-install into MOODLE_21_STABLE
weekly release 2.1.8+
MDL-25948 upgrade: Check that field does not match defaults before editing.
Merge branch 'MDL-25948_m21' of git://github.com/markn86/moodle into MOODLE_21_STABLE