[PATCH] build: require perl 5.6

This reduces the implicit requirement from 5.6.2 back to 5.6,
while raising the explicit requirement to match the actual code.

* configure.ac (PERL): Fail up front if perl is too old.
* NEWS: Document this.
* README: Likewise.
* README-hacking: Likewise.
* lib/Autom4te/ChannelDefs.pm: Likewise.
* lib/Autom4te/General.pm: Likewise.
---

I'm pushing this to match our recent decisions, and to match automake's
insistence on 5.6.

 NEWS                        |    4 +++-
 README                      |    2 +-
 README-hacking              |    2 +-
 configure.ac                |    4 ++--
 lib/Autom4te/ChannelDefs.pm |    2 +-
 lib/Autom4te/General.pm     |    2 +-
 6 files changed, 9 insertions(+), 7 deletions(-)

diff --git a/NEWS b/NEWS
index 7447229..dbc19dc 100644
--- a/NEWS
+++ b/NEWS
 <at>  <at>  -1,7 +1,9  <at>  <at> 
 GNU Autoconf NEWS - User visible changes.

-* Noteworthy changes in release ?.? (????-??-??) [?]