Improve bulk.t standalone server detection
Don't test fsync locking against mongos
replace hard coded error codes with descriptive macros
PERL-336 don't throw exceptions on command queries

Prior to this commit, the Cursor.xs code threw an exception if it saw
'$err' in a document.  This prevents command responses from being
returned, which prevents inspection of the code returned with the
error, if any.

This commit only throws on '$err' for collections other than '$cmd'.
skip parallel scan on mongos
fix getLastError test for mongos
skip some text search tests on 2.4 mongos
fix bad command test