use a hash for compiled stems, to avoid spurious duplicates.
adjust find_updatenames accordingly.

support code for pkg_add -u:
- distant_available(), using the distant listing functions.
- stem compiler, to match lots of stems

split PackageName handling into PackageName stuff/PkgSpec matching.
Kill new method that isn't really used.

Name explicit splitstem() to get the stem of a packagename.

Adjust calls to the interface.

unified headers, switch to smaller copyright notice.

move wildcard rewriting down. Allows flavors in package-specs to
properly contain a dot and other fun characters.

Reported by Jason Ish. Survives a full ports build.

url2pkgname as an explicit function

Add is_stem/find_stem

new import of my pkgtools, after a slight naming disagreement with the
Upper Management...