libpqxx: update to 4.0

[ryandesign@…]

$ port livecheck libpqxx
libpqxx seems to have been updated (port version: 3.0.2, new version: 4.0)

[ryandesign@…]

proposed patch

[ryandesign@…]

Attached is a patch to update libpqxx to version 4.0.

• Removed the unnecessary distname line.
• Updated to rmd160/sha256 checksum types.
• Added variants for postgresql83/84/90/91, making 91, the current stable version, the default; left old pq83 variant to help users upgrading; this variant should be removed after everyone has upgraded, for example in one year.
• Patched maketemporary to avoid an error message about improper use of the mktemp command; apparently maketemporary is designed to call mktemp various ways, some of which may be improper, as it attempts to determine how to use it properly; we don't want to see those errors in the configure phase output.
• Patched splitconfig to avoid usage of "echo -n" which is not POSIX-compliant, thus causing incorrect output on Snow Leopard and later.
• Patched configure on darwin to fix incorrect assumption that true and false always live in /bin; on OS X they live in /usr/bin.

In addition I believe this fixes the build failure with clang reported in #32689.

I believe these changes are ready to be committed.

[ryandesign@…]

r91294