pkgIndex: move package require to usage files

TCL advises against putting require statements in the index file.

    http://wiki.tcl.tk/5900

Errors like these can otherwise happen:

error reading package index file pkgIndex.tcl: too many nested
evaluations (infinite loop?)
pkgIndex: remove reference to none existing file expect.tcl
Merge pull request #14 from neg/pkgindex

Pkgindex