* fpc_val_real_shortstr: track amount of digits in mantissa and limit integer exponent values. This does not (yet) prevent floating-point overflows, but is a necessary step to prevent them.

git-svn-id: http://svn.freepascal.org/svn/fpc/trunk@25549 3ad0048d-3df7-0310-abae-a5850022a9f2