OPENIG-133 Fix the ContentLengthHeader behavior about negative values.

- Negatives values are no longer registered.
- Reactivated corresponding unit test.

git-svn-id: https://svn.forgerock.org/openig/trunk@642 dbb9e58e-28e6-4ce0-90e8-f11d9605b710
CR-4937 OPENIG-312 Updated troubleshooting section.
- Updated stacktrace in section 1.
- Remove section 2.
- Replaced section 'Unexpected character  at position 1103' and replaced it by
'Extra or missing character / invalid JSON'

git-svn-id: https://svn.forgerock.org/openig/trunk@643 dbb9e58e-28e6-4ce0-90e8-f11d9605b710