Security update OpenEXR and ilmbase to 2.2.1.
While here, fix libIlmImfUtil_la_LDFLAGp so that when linking libIlmImfUtil,
the locally built libIlmImf gets precedence over the one in /usr/local,
to permit upgrades in a running system with the older version installed.
This changes the library's SONAME, so bump PORTREVISION of all dependees.
Unfortunately, this looks a bit too intrusive for an MFH to 2017Q4.