net-analyzer/pnp4nagios: new revision to fix nagios/icinga "or" dependency.

net-analyzer/pnp4nagios: new revision to fix nagios/icinga "or" dependency.

Previous revisions of pnp4nagios have an "or" dependency on either
Nagios or Icinga,

  || ( net-analyzer/nagios-core net-analyzer/icinga ...

The way "or" dependencies work is that they are considered satisfied
if any elements of the associated group are installed. Thus the above
stanza allows Nagios and Icinga to be swapped out without rebuilding
pnp4nagios. That is incorrect, since later in the ebuild, nagios-
or icinga-specific paths are compiled into pnp4nagios.

The usual solution to that problem is to choose a default package that
satisfies the "one of these" dependency, but to allow the user to
specify one with a USE flag. This new revision adds three USE flags:
icinga, icinga2, and nagios. The "nagios" flag is enabled by default,
and builds pnp4nagios against net-analyzer/nagios. The other flags
build against the associated package.

In the process, the dependency on nagios-3.x was loosened to accept
nagios-4.x as well. The nagios-3.x series has been end-of-life'd, and
has multiple open security bugs.

Bug: https://bugs.gentoo.org/628086
Bug: https://bugs.gentoo.org/629380
Bug: https://bugs.gentoo.org/636234
Closes: https://bugs.gentoo.org/600424
Package-Manager: Portage-2.3.8, Repoman-2.3.3