fparseln(3): Update from NetBSD sources.

-fix a condition so that fparseln() doesn't report spurious empty lines
 eg after 2 comment lines, or on EOF after a single comment line
-no escape character means no escaped characters

modify the previous fix so that no pointless realloc()s are done in
the case of multiple empty continuation lines, and comment the code
to make the logics obvious

fparseln is now part of libc in NetBSD so this changes the previous
revision numbering.

Obtained from:	NetBSD (CVS Rev. 1.6-1.7)
MFC after:	2 weeks
Fix mismatch.

MFC after:	3 days