pgsql: Remove equals sign from environment variable with not defaults

Log Message:
-----------
Remove equals sign from environment variable with not defaults for
configure.

Modified Files:
--------------
pgsql/doc/src/sgml:
installation.sgml (r1.255 -> r1.256)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/installation.sgml.diff?r1=1.255&r2=1.256)