configure.ac: Auto-detect symbol versioning

Instead of relying on the --with-symbol-versioning flag, automatically
detect if we can use it.

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
configure.ac: Remove unnecessary checks

If we're not using the result of a test, the test should not be there at
all: drop a few IPv6 related checks from configure.ac.

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
Release libmongo-client 0.1.8

Added NEWS items for 0.1.8, bumped the version in configure.ac, and
updated the library version in src/Makefile.am.

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
Merge branch 'release/0.1.8' into stable
Merge tag 'libmongo-client-0.1.8'

libmongo-client 0.1.8 release