* vhdl-mode.texi: Add "@documentencoding UTF-8",

since this is a toplevel .texi file.
* configure.ac (AC_CONFIG_MACRO_DIR): Use it.
Use pkg-config's pkg.m4

* configure.ac: Use pkg-config's pkg.m4, rather than reinventing it.
Add explicit AC_SUBST's where needed.

* autogen.sh (progs): Add pkg-config.
(pkg_config_min): New variable.

* INSTALL.REPO: Mention pkg-config.

* etc/PROBLEMS: Mention a related issue that can occur with a local automake.
Remove the --with-pkg-config-prog configure option

* configure.ac (--with-pkg-config-prog): Remove.
Use the PKG_CONFIG environment variable instead if you need it.

* etc/NEWS: Mention this.
* configure.ac (PKG_CONFIG_PATH): Declare with AC_ARG_VAR.