autoconf: Checks for some programs

autoconf: Checks for some programs

./configure script checks now for the following programs:
 * CC  - using AC_PROG_CC
 * AR  - using AC_CHECK_TOOL among ar
 * TAR - among gtar, tar

Checks not implemented:
 * INSTALL  - needs install-sh or install.sh in sources
 * RPMBUILD - not known alternatives for rpmbuild
 * PYTHON   - no PYTHON variable in Makefile,
              has to set NO_PYTHON if not present

Signed-off-by: Jakub Narebski <jnareb@gmail.com>
Signed-off-by: Junio C Hamano <junkio@cox.net>