Follow-up to r1483535:  In case of overflow, return the start pointer
in *ENDPTR.  Also, fix the overflow condition.

Extend the test cases to cover the range checking corner cases.

* subversion/libsvn_subr/types.c
  (svn_revnum_parse): fix overflow detection and error behavior

* subversion/tests/libsvn_subr/revision-test.c
  (test_revnum_parse): add range check corner cases


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1483545 13f79535-47bb-0310-9956-ffa450edef68