Replace char class :space: with explicit chars

Replace char class :space: with explicit chars

Some major distributions are still using 'mawk' and they are not using
the latest version - we end here with hidden dependency on the latest
version of mawk (1.3.4) while i.e. Debian Lenny seems to stay with 1.3.3.
So we end with completely broken  vgimportclone script on such system.

We would need to check for proper support of :space: and abort build if
it doesn't work or simplier replace [:space:] with [ \t] which seems
sufficient to make it work (as can be seen in this patch)

A better fix would be to use command line parameter override - leaving
as FIXME comment.

This patch makes t-vgimportclone.sh test passing on Lenny.