[PATCH + 8.3] Don't derive partial_symbol from general_symbol_info

[Tom Tromey]

>>>>> "Tom" == Tom Tromey <tom@tromey.com> writes:

Tom> This patch partly reverts commit 8a6d42345 ("Change representation of
Tom> psymbol to flush out accessors"); specifically, it changes
Tom> partial_symbol to no longer derive from general_symbol_info.

[...]
Tom> Regression tested by the buildbot.  I think this should go in 8.3 as
Tom> well.

I'm going to push this now.

Tom