Reimplemented much of <istream> such that single character extractions do not...

Reimplemented much of <istream> such that single character extractions do not check to see if this is the last character in the stream and thus never set eofbit.  This fixes http://llvm.org/bugs/show_bug.cgi?id=10817 .  This fix requires a recompiled libc++.dylib to be fully implemented.  The recompiled libc++.dylib is ABI compatible with that shipped on Lion.

llvm-svn: 138961