Rework -Si display logic
We did some funny stuff here before to allow specifying fully-qualified
package names, such as 'testing/gcc' or 'core/gcc'. However, it was done
by duplicating code, not to mention an early escape if a repository
could not be found for an early target. Something like `pacman -Si
foo/bar core/gcc' would not give expected results, although `pacman -Si
bar gcc' would.
Clean up the code, remove strncpy() usage, and clarify the error
messages a bit.
Signed-off-by: Dan McGee <dan@archlinux.org>