Added the ability to sign extend a Scalar at any bit position for integer

types.

Added the abilty to set a RegisterValue type via accessor and enum.

Added the ability to read arguments for a function for ARM if you are on the
first instruction in ABIMacOSX_arm.

Fixed an issue where a file descriptor becoming invalid could cause an 
inifnite loop spin in the libedit thread.

llvm-svn: 131610