[PATCH 0/7] Use warn_unused_result on release methods

[Tom Tromey <tromey at adacore dot com>]

This applies the warn_unused_result attribute to various "release"
methods in gdb.  The idea here is to avoid the bug where "release" is
used when "reset (nullptr)" is meant.

This caught one bug, so I consider it a success.  Perhaps the new
attribute can be used elsewhere as well.

Tested by the buildbot.
Let me know what you think.

thanks,
Tom