Cost of AtEOXact_Buffers in --enable-cassert

Hi,

I do test (and even run) some stuff running with cassert enabled. For many 
things the reliability and performance is ok enough and its useful, especially 
if you have your own c functions and such.
Imho thats useful as it makes catching some bugs more likely...

The most prohibitively expensive part is the AtEOXact_Buffers check of running 
through all buffers and checking their pin count. And it makes $app's 
regression tests take thrice their time...

Would somebody object agains putting those in an extra define so that those can 
be disabled in pg_config_manual? Or even disable it by default entirely...

Andres