Added updates from Jared Hancock.

Added updates from Jared Hancock.

Fixed error output from disabling global flags with -D. Added --remove
option and left --prune as an alias

Also, as requested, pruning a flag no longer removes it from local
package.use unless an explicit package is given. Unfortunately, package
wildcards are not yet supported, so the package must be given exactly
as it is found in package.use.

Emit a warning for invalid package atoms:

euse -E ldap -p =net-misc/openssh
euse -E ldap -p net-misc/openssh-5.6*

will both fail now since they would be ineffective and give further
warnings from portage later.

euse also would add an extra empty line to make.conf every time it was
invoked with -E or -D