Fix #8017: allow username up to 255 chars

Signed-off-by: Paul Richards <paul@mantisforge.org>
Allow realname up to 255 chars

Signed-off-by: Paul Richards <paul@mantisforge.org>
Allow password up to 64 chars

This enables future use of cryptographic hash algorithms such as bcrypt,
Whirlpool, sha512 or RipeMD.

Signed-off-by: Paul Richards <paul@mantisforge.org>
Allow email up to 255 chars

Maximum allowed length is actually 254. Reference:
http://stackoverflow.com/questions/386294/what-is-the-maximum-length-of-a-valid-email-address

Signed-off-by: Paul Richards <paul@mantisforge.org>