Reset CFLAGS and CXXFLAGS to a previous value to fix the large release builds.

[blast007]

We noticed that release builds on Linux (and possibly other platforms that use autotools) were including debugging information in the binaries. This change stops the -g compiler option from being automatically added to release builds. Issue #263 reported part of the problem.

[blast007]

I'll need to take a close look at the configure.ac file. I do see now that the user_* options are only initialized when in debugging mode, but I could just always init those. I'll poke around with it some more to see if I can figure out why it's adding -g in the first place.