Revert "check if ImageMagick is in PATH"
Revert "check if ImageMagick is in PATH"

This makes it harder to add a custom (non-ImageMagick) processor and fails
on gratuitously Windows.

This reverts commit fb9a4d609387f8e33151042bbca0e0d1f812db83.

Conflicts:

	init.rb

norman/has_image