Using XLogFileNameP in critical section

Hi,

I encountered that the assertion error is reported instead of a proper
PANIC message when failed to fsync WAL. The cause is that there are
multiple places where we call XLogFileNameP function that calls palloc
during critical section, for example XLogWrite function.

TRAP: FailedAssertion("CritSectionCount == 0 ||
(context)->allowInCritSection", File: "mcxt.c", Line: 956)

As far as I can see there are five places we need to fix.I've attached a patch.

Regards,

--
Masahiko Sawada            http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services