ENH: Moved kwsys_ns and kwsysEXPORT macros to Configure.h in the case of building a kwsys source file.  This allows more than one header to be included in a kwsys source file without redefining the macros.

BUG: Do not increment optr by 2 after storing only one character.  Also fixed possibility of storing uninitialized characters from the last triplet.

COMP: Adding work-around for CMake dependency scanning limitation.  Any configured header included by KWSYS_HEADER() in a .c or .cxx file in kwsys itself must use this hack to get dependencies.

ENH: Added use of KWSYS_HEADER macro in c and cxx files to include kwsys headers through their configured namespace.

ERR: Added casts to remove type conversion warnings.  Pointer differences can be 64-bit, but unsigned long is 32-bit on many platforms.  We know we are not traversing more data than can be handled by an unsigned long, though, because the length argument is an unsigned long.