rpm 5.4.0: respect to the arch when choose the alternatives

rpm 5.4.0: respect to the arch when choose the alternatives

There is a bug if we:
1) bitbake diffutils with MACHINE=crownbay
2) bitbake diffutils with MACHINE=qemux86
3) bitbake core-image-sato with MACHINE=crownbay

Then the diffutils.i586 would be installed to the crownbay's image, this
is because diffutils.i586 is newer than diffutils.core2, and rpm doesn't
respect to the arch priorities:

We have put the archs in order in _solve_dbpath:

crownbay/solvedb:core2/solvedb:i586/solvedb:all/solvedb

Fix rpm to respect to the order, for example, if it finds a pkg in both
core2/ and i586/, and the core2/ comes first, it should not use the one
in i586/ even if it's build time is newer.

Note: Don't worry about the _free(*ptr), it can check whether ptr is
NULL or not.

This is for the denzil branch, and the master branch also needs it.

[YOCTO #2360]

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>