[BUILD] Allow interworking of thumb on different platforms.
[PROCESS] Implemented simple bitmap allocation of file-descriptors for libc/posix integration.
[MM] Fix error for finding segments within the vm maps.
[MM] bt_page - Fixed total memory size added to the default memory pool.
[FS] BT_Open() mode is now a set of flags, with a new BT_GetModeFlags() routine to convert from a string to flags.
[SHELL] Upgraded shell and commands to use the modified BT_Open() api.