add a .gitignore file with similar contents to .cvsignore, to help users

of git conversions of the tree. suggested by f.holop, ok jca@

as pointed out by semarie@, got doesn't support this syntax, but it parses
.cvsignore as well anyway so that's not important.

.gitignore

@@ -0,0 +1,13 @@
+/bulk/
+/distfiles/
+/locks/
+/logs/
+/lost+found/
+/mystuff/
+/openbsd-wip/
+/packages/
+/plist/
+/pobj/
+/sqlports/
+/sqlports-journal/
+/update/