The patch fixes a rare bug that may occur when one tries to vacuum a single

table. The table name is de-allocated by the CommitTransactionCommand()
in vc_init() before it is copied in VacRel.data and sometimes this causes
a SIGSEGV. My patch simply moves the strcpy before vc_init.

Submitted by Massimo Dal Zotto <dz@cs.unitn.it>.