pgsql: Document that we need to update the ecpg regression files when we

Log Message:
-----------
Document that we need to update the ecpg regression files when we update
the library version number.

Modified Files:
--------------
pgsql/src/tools:
RELEASE_CHANGES (r1.70 -> r1.71)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/tools/RELEASE_CHANGES.diff?r1=1.70&r2=1.71)