fix getservby*_r result pointer value on error

this is a clone of the fix to the gethostby*_r functions in
commit fe82bb9b921be34370e6b71a1c6f062c20999ae0. the man pages
document that the getservby*_r functions set this pointer to
NULL if there was an error or if no record was found.

make getservby*_r return error code rather than -1 (and using errno)

untested but should be correct..

fix getservby*() with null pointer for protocol argument

not sure this is the best fix but it should work

remove some stray trailing space characters

initial check-in, version 0.5.0