Report version of Mac OS X in configuration log

If we are building on Mac OS X, use the official operating system
version (e.g. 10.8) instead of the kernel version (e.g. 12.4).
Only install debug symbols if they are in separate file

If the strip utility is not present, debug symbols won't be in a
separate file and subsequently cannot be installed.
Refactor code to separate extensions from filename

The earlier code assumed that the version information always follows
the full file path; this code splits the path up into various parts
so that this may be changed.
Strip debug symbols to separate file on MacOS X

The standard Xcode toolchain on MacOS X uses strip and dsymutil, not
objcopy as the GNU toolchain does.
Always keep debug bundle near executable on Mac OS X

There isn't a /usr/lib/debug directory as on Linux.
Remove linker command from compiler command-line

There is no SuiteSparse headers or libraries in
/System/Library/Frameworks/Accelerate.framework on MacOS X, so adding
this directive won't contribute anything other than compiler warnings.
Use libc++ runtime if necessary for C++11 compliance

If we are using the Apple toolchain on MacOS X, we must use the
newer runtime and not the old GCC 4.2 fork, in order to get the
C++11 library features (such as std::shared_ptr).
Remove bash4-isms from configuration script

Getting uppercase of a string can be done in a way that is compatible
with Bash 3.2. This creates a dependency on the `tr` utility, but I
reckon it will/can be available everywhere Bash 3.2 is.
Merge pull request #334 from rolk/334_macver

Support configuration on MacOS X using Apple toolchain