Log Message:
Create new variables INCOMPAT_ZLIB, INCOMPAT_BZIP2, INCOMPAT_READLINE,
INCOMPAT_GETTEXT that are analogous to INCOMPAT_ICONV and contain lists of
shell wildcards intended to match against ${MACHINE_PLATFORM}.  These
variables are used to note those platforms that have the named packages in
the base system but are incompatible in some way from the pkgsrc version
of the same package.  Change INCOMPAT_CURSES to have the same sematics as
above.  These variables allow much greater precision in specifying which
platforms have broken (for the purposes of pkgsrc) versions of software in
the base system that must be ignored.

The buildlink.mk files for these packages define private _INCOMPAT_*
versions of these variables, and they contain the default lists of
platforms that are known to have incompatible software bits.

This addresses pkg/17775 submitted by Julien T. Letessier
<julien.letessier at sun dot com>.