autotools: use /usr/bin/perl in shebang

Signed-off-by: David Abdurachmanov <davidlt@cern.ch>
Merge pull request #649 from davidlt/autotools-fix-perl-path-v2

Autotools fix perl path v2
Merge remote branch 'origin/IB/CMSSW_7_1_X/stable' into IB/CMSSW_7_0_X/stable