On VMS, stdout may very well lead to a file that is written to in a

On VMS, stdout may very well lead to a file that is written to in a
record-oriented fashion.  That means that every write() will write a
separate record, which will be read separately by the programs trying
to read from it.  This can be very confusing.

The solution is to put a BIO filter in the way that will buffer text
until a linefeed is reached, and then write everything a line at a
time, so every record written will be an actual line, not chunks of
lines and not (usually doesn't happen, but I've seen it once) several
lines in one record.  Voila, BIO_f_linebuffer() is born.

Since we're so close to release time, I'm making this VMS-only for
now, just to make sure no code is needlessly broken by this.  After
the release, this BIO method will be enabled on all other platforms as
well.