invalid search_path complaints

If you use ALTER ROLE/DATABASE SET to configure an invalid
search_path, PostgreSQL 9.1 issues a complaint about the invalid
setting on each new connection. This is a behavior change relatively
to previous releases, which did not. git bisect blames this commit:

2594cf0e8c04406ffff19b1651c5a406d376657c is the first bad commit
commit 2594cf0e8c04406ffff19b1651c5a406d376657c
Author: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Date: Thu Apr 7 00:11:01 2011 -0400

Revise the API for GUC variable assign hooks.

The previous functions of assign hooks are now split between check hooks
and assign hooks, where the former can fail but the latter shouldn't.
Aside from being conceptually clearer, this approach exposes the
"canonicalized" form of the variable value to guc.c without having to do
an actual assignment. And that lets us fix the problem recently noted by
Bernd Helmle that the auto-tune patch for wal_buffers resulted in bogus
log messages about "parameter "wal_buffers" cannot be changed without
restarting the server". There may be some speed advantage too, because
this design lets hook functions avoid re-parsing variable values when
restoring a previous state after a rollback (they can store a pre-parsed
representation of the value instead). This patch also resolves a
longstanding annoyance about custom error messages from variable assign
hooks: they should modify, not appear separately from, guc.c's own message
about "invalid parameter value".

Is this an intentional change? And is it desirable?

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company