re: xsrc/50093 (7.0_RC1 Xorg server gets SIGSEGV on exit)

[matthew green <mrg%eterna.com.au@localhost>]

i'm pretty sure this was fixed with the Mesa destructor fixes
that were pulled up:

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RCS file: /cvsroot/xsrc/external/mit/MesaLib/dist/src/util/ralloc.c,v
revision 1.1.1.1.2.3
date: 2015-09-04 07:57:47 -0700;  author: martin;  state: Exp;  lines: +1 -2;  commitid: PhZmqy6derWbKWzy;
Pull up the folowing revisions (requested by mlelstv in #954):

        xsrc/external/mit/MesaLib/dist/src/util/ralloc.c        1.2

Use __attribute__((__destructor__)), not atexit, in shared objects.

Recovered from our local changes to MesaLib7.
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.mrg.