Fix two ParseInt edge cases

1) ParseInt and ParseUint accept strings that have spaces followed by
   a valid number, however the base check for determining hex numbers
   does not take this into account currently, but now does this this
   change.
2) ParseUint rejects negative numbers except in the case that the
   template argument is unsigned long long.  That is a mistake; it
   should reject negative numbers in all cases and this change does
   that by rejecting any string with a - prefix.

Bug: 112668205
Test: new (and old) unit tests
Change-Id: I0179b42e50adc1b169cf0e6d830283b71210a029