Add script to check man page references

This script checks for some of the most obvious mistakes when formatting
man page references (which should have the form “**ganeti**\(7)”). While
this works now, it is very hard to avoid ambiguities (e.g. references
within verbatim blocks) when using regular expressions.

Also fixes a typo in Makefile.am by replacing “harcoded” with
“hardcoded”.

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: Guido Trotter <ultrotter@google.com>