Look for package names in a case-insensitive way

[ChrisJefferson]

In GAP 4.11 and earlier, packages were often mixed case, in 4.12 they are always lower case.

This looks for packages case-insensitively, so they can be found in all versions of GAP.

[fingolfin]

Remember to also update resp. add tags

[wilfwilson]

Looks like that's done