Change NFSv4.1 and NFSv4.2 error strings to start with lower case letter.

r356084 added error strings for NFSv4.1 and NFSv4.2, with the first
character capitalized. Since the other error strings were not capitalized
and these strings would usually be imbedded in an error, I decided to
make the first characters lower cased.
No real effect but more consistent.