feat(shell/CMakeLists.txt): Multi-platform Support

Now we require Bison-2.3 and above, and Flex 2.5.35 and above.

For OSX we use FlexLexer_osx.h instead due to header incompatibility
issues[1]

[1] https://bugs.launchpad.net/zorba/+bug/1034582
feat(shell/CMakeLists.txt): Multi-platform Support