ENH: Make C++11 try_compile result related to CMAKE_CXX_FLAGS

If the CMAKE_CXX_FLAGS change then the C++11 try compile will be
re-done. This is done by computing the MD5 checksum of the flags, and
using that as part of the variable name in the cache.

Also changing variables to lower case, and removing extra CMAKE_ save
variable in function.

Change-Id: I61bb662e8bb1550f9db1960d872d064053ecc9d8
Enable C++11 with libc++

Automatically add -std=c++11 to the required flags to enable the
tr1 features needed. This is for XCode 5.0 with clang 5.0 with libc++,
which is missing the tr1 features with the default compilation
options.

Change-Id: Ic2ec35e4db526de95ca2a80e4a4a4b23159d9cb9
Add required CMake flags to our own project and the Examples

Change-Id: I3fcfe86659fca3ddaa4a7e08cec0eb2b2b52c43e
Move Version CMake block to the beginning of CMakeList.txt

This make the SimpleITK version be one of the first lines cmake prints.

Change-Id: If8dbfae0d87a4470ca30174de150e69e66bbf697
Check that std=c++11 is not already a required flag before testing

Change-Id: I0fb0b8d59870c18bed42bfd681346eb7a980203c
Add "-std=" and "-stdlib=" flags to the required flags.

If CMAKE_CXX_FLAGS already contain either of these, they should be
moved to the SimpleITK's required flags.

Change-Id: Ia8ead58ee37cafe7c5223cc74d8838c998d0e9c7
Merge topic 'SIMPLEITK-480_AddCXX11FlagForOSXMavericks' into next

3964df66 Add "-std=" and "-stdlib=" flags to the required flags.
03e4de9f Check that std=c++11 is not already a required flag before testing
442b178d Move Version CMake block to the beginning of CMakeList.txt
e350b1b3 Add required CMake flags to our own project and the Examples
debf194f Enable C++11 with libc++
4ac3904d ENH: Make C++11 try_compile result related to CMAKE_CXX_FLAGS