Use named captures in Catalog::ParseHeader()

Use named captures in Catalog::ParseHeader()

Using at least perl 5.14 is required since 4c15327, meaning that it is
possible to use named captures and the %+ hash instead of having to
count parenthesis groups manually.

While on it, CATALOG is made more flexible in its handling of
whitespaces for parameter lists (see the addition of \s* in this
case).  The generated postgres.bki remains exactly the same before and
after this commit.

Author: Dagfinn Ilmari Mannsåker
Reviewed-by: John Naylor
Discussion: https://postgr.es/m/87y1l3s7o9.fsf@wibble.ilmari.org