opensc @0.23.0: Package libeac was not found in the pkg-config search path

[ryandesign (Ryan Carsten Schmidt)]

Looks like opensc would use libeac if it existed in MacPorts and were installed:

​https://build.macports.org/builders/ports-10.6_x86_64-builder/builds/170734/steps/install-port/logs/stdio

configure: WARNING: libeac not found by pkg-config
checking for eac/eac.h... no
configure: WARNING: OpenPACE headers not found
checking for EAC_CTX_init_pace... configure: WARNING: Cannot link against libeac
checking for EAC_OBJ_nid2obj... no
Package libeac was not found in the pkg-config search path.
Perhaps you should add the directory containing `libeac.pc'
to the PKG_CONFIG_PATH environment variable

A configure argument should be used to explicitly disable libeac so that, if it is ever added to MacPorts, this port won't suddenly start using it.