Fix reaches end of function error
Check for C++11 support, fail if it's not there.
Add dependency on Boost.
Add optional use of Google Profiler.

See https://code.google.com/p/gperftools
Don't override CFLAGS, CPPFLAGS, etc.

Doing so gives the hardcoded values precedence over the user's environment.
Use AM_CFLAGS, AM_CPPFLAGS, etc. instead.
Better test for conflict between optimization and FORTIFY_SOURCE
Disable C++11 deprecation warning for register storage class

It's used in GLib, so we're stuck with it for the short term.
Added a GUID test suite

The plan is to change gnc guid to use boost's guid implementation. There were
no tests for guid before, but we need them to ensure that we don't have regressions
when that work begins.
Allow C/C++ extensions

MinGW declares any standard functions not part of the ISO C standard
in #ifndef __STRICT_ANSI__ blocks; Gcc defines __STRICT_ANSI__ with
-std=c++11; Pass 'ext' to the C++11 macro to get -std=gnu++ll, which allows
all those extensions we use.