Allow for building specific package

Several packages may be built from the same source all in one how.

As long as the makefile rules match the package name from the subpackage name, then they can be built individiaully, i.e.

"mksolpkg -p ALTovagent" requires
Files:
- solaris_pkg/pkginfo.ALTovagent
Makefile rules for
- make ALTovagent
- make install-ALTovagent

Any solaris_pkg files with the posstfix of the package name will be used for that package