This tests dlopens and resolves all symbols to make sure there are no missing
symbols in our provider modules.

We checked only header file "sys/inotify" for detection whether inotify
works. Some platforms do not have built in inotify, but contain library,
which provides inotify-compatible interface.

This patch adds more robust detection of inotify in configuration time and
appends linker flags to Makefile if inotify is provided by library.

We used pkg-config only as a fallback if header files was not found,
but detection of library failed in case of available header file and
linking problem (missing -Ldir).

This patch prefers pkg-config.

We check whether HAVE_INTPTR_T is defined in definition of macro
discard_const_p, but autootols macro AC_CHECK_TYPE did not generate it.

If $libdir is not in default library path libunistring cannot be
found. (pkg-config can not be used in this case).
This patch helps to search libunistring in "$libdir" directory.

In refactoring part, indentation was updated to be more readable
and some duplicated parts were removed.

Function gettext needn't be included in libc, it can be part of another
library. Autotools macro AM_GNU_GETTEXT generate makefile variables
(LIBINTL, LTLIBINTL), which contain necessary linker flags.

checking for GNU gettext in libc... no
checking for iconv... yes
checking for GNU gettext in libintl... yes
checking whether to use NLS... yes
checking where the gettext function comes from... external libintl

AC_MSG_RESULT was not used everywhere after AC_MSG_CHECKING.
Therefore two lines from configure output was mixed in some cases.

Detect directory with python libraries and add this
directory to the list of directories to be searched for linker.