Adds locale-independent str[fp]time() to system
Adds locale-independent str[fp]time() to system

Adds core.system.strftime() and core.system.strptime() that always use
the C locale.

Warning: these are not thread-safe!

minesense/VisTrails,hjanime/VisTrails,minesense/VisTrails,hjanime/VisTrails,Nikea/VisTrails,hjanime/VisTrails,VisTrails/VisTrails,VisTrails/VisTrails,celiafish/VisTrails,hjanime/VisTrails,VisTrails/VisTrails,Nikea/VisTrails,Nikea/VisTrails,minesense/VisTrails,VisTrails/VisTrails,minesense/VisTrails,minesense/VisTrails,celiafish/VisTrails,hjanime/VisTrails,Nikea/VisTrails,celiafish/VisTrails,VisTrails/VisTrails,celiafish/VisTrails