Reduce number of packages install_prereq installs on Debian systems.

'search' will look for any package containing the name provided, so we need to
force a more exact search.
........

Merged revisions 379276 from http://svn.asterisk.org/svn/asterisk/branches/1.8


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/11@379277 f38db490-d61c-443f-a65b-d21fe96a405b