Allow uppercase variant of package root also

Both the straight-forward mod-ule_ROOT variable and the more idiomatic
MOD_ULE_ROOT variant are allowed when specifying where to look for a
package.
Allow common _ROOT suffix in addition to original _PREFIX
Consolidate package location variables

Always use the same form of package location variable, to maintain
consistency.
Use uppercase for the shared-object variable as well
Reuse the uppercase variant across the entire function
Merge pull request #166 from rolk/166_upcase

Use uppercase consistently in configuration variable names