build-sys: use pkg-config to locate dependencies

This commit alters XRANDR (X Resize And Rotate) extension dependency,
which is expected to have at least version 1.4.  Earlier old versions of
xrandr were supported, at least to some extent.
build-sys: add test programs to .gitinore file
build-sys: unify configure.ac syntax
build-sys: use iconv library detections from gettext

This patch took copy of config.rpath from gettext 0.18.2 to build-aux/
directory.  Software projects usually does not need to do that, because
the file is copied by gettext autopoint in autogen.sh or bootstrap.#

In Fluxbox case calling autopoint seems wrong, as it would generate po/
directory with necessary make automation, adn 'msgid' & 'msgstr' files,
but that is not how the translations are done in this project.