Make reformat-dat-files, reformat-dat-files VPATH safe.
Make reformat-dat-files, reformat-dat-files VPATH safe.

The reformat_dat_file.pl script, added by 372728b0d49552641, supported
all the necessary options to make it work in a VPATH build, but the
makefile invocations didn't take VPATH into account. Fix that.

Discussion: 79d6a2275cdf2a09860f6376b28d7099c10ca0f3@alap3.anarazel.de
Backpatch: 11-, where 372728b0d49552641 was merged

adam8157/gpdb,lisakowen/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,lisakowen/gpdb,greenplum-db/gpdb,lisakowen/gpdb,50wu/gpdb,xinzweb/gpdb,xinzweb/gpdb,greenplum-db/gpdb,xinzweb/gpdb,greenplum-db/gpdb,adam8157/gpdb,adam8157/gpdb,adam8157/gpdb,xinzweb/gpdb,50wu/gpdb,lisakowen/gpdb,adam8157/gpdb,lisakowen/gpdb,50wu/gpdb,xinzweb/gpdb,xinzweb/gpdb,xinzweb/gpdb,greenplum-db/gpdb,adam8157/gpdb,lisakowen/gpdb,lisakowen/gpdb,50wu/gpdb,xinzweb/gpdb,lisakowen/gpdb,50wu/gpdb,50wu/gpdb,adam8157/gpdb,50wu/gpdb,adam8157/gpdb,greenplum-db/gpdb,50wu/gpdb,greenplum-db/gpdb