jtv/libpqxx 7.1.2

libpqxx 7.1.2: Almost not a patch release

on GitHub

Lots of changes here, some important:

• Document build in BUILDING-configure.md / BUILDING-cmake.md.
• Work around silly clang warning in test_errorhandler.cxx.
• Fix install error with some internal headers. (#322)
• Fix "No object selected" error message in large objects. (#324)
• If error has no SQLSTATE, throw broken_connection. (#280)
• Fix argument order in encrypt_password. (#333, #334)
• Fix underestimate of buffer size for to_string for floats. (#328)