Revision 1574710

Kick off work on pkg-config support (issue #738, and also #4435).

pkg-config support allows API consumers on UNIX-like systems to link
to Subversion libraries without having to manually specify the correct
set of linker flags, including the particular flags for dependencies
required by a particular build of Subversion (bdb, serf, etc.).
pkg-config uses libsvn_foo.pc files which describe the set of flags
required to link to libsvn_foo.
See http://www.freedesktop.org/wiki/Software/pkg-config/ for more information.

Make gen-make.py produce .pc.in files for all Subversion libraries,
and make the configure script produce .pc files from these .pc.in files.
Dependency declarations and linker flags are based on information
parsed from build.conf.

Dependencies of Subversion which support pkg-config can be marked
as such in build.conf, allowing pkg-config to resolve them. The
name of the dependency's pkg-config script has to be specified
without the .pc extension, e.g.:

 [gnome-keyring]
 type = lib
 external-lib = $(SVN_GNOME_KEYRING_LIBS)
 pkg-config = gnome-keyring-1

Dependencies not aware of pkg-config are added to linker flags directly.

To illustrate, the generated libsvn_client.pc file on my system contains:

[[[
  prefix=/home/stsp/svn/prefix/svn-trunk
  exec_prefix=${prefix}
  libdir=${exec_prefix}/lib
  includedir=${prefix}/include
  
  Name: libsvn_client
  Description: Subversion Client Library
  Version: 1.9.0
  Required:  apr-1
  Required.private: 
  Libs: -L${libdir}  -lsvn_wc -lsvn_ra -lsvn_delta -lsvn_diff -lsvn_subr
  Cflags: -I${includedir}
]]]

There is no support for optional dependencies between Subversion libraries
yet, however. For instance, libsvn_client might or might not be linked to
libsvn_ra_serf. Such dependencies are currently omitted. Also, I'm not
sure yet what to do in cases where a dependency might be statically or
dynamically linked, e.g. sqlite.

The .pc files are not being installed yet. I don't want to expose these
files to systems using pkg-config until all outstanding issues are resolved.

* build/generator/gen_make.py
  (Generator.write): Generate .pc.in files.
  (Generator.write_pkg_config_dot_in_files): New helper function.

* build/generator/templates/pkg-config.in.ezt: New file, the .pc.in template.

* build.conf: apr, apr-util, serf, gnome-keyring, and sqlite support pkg-config.
   There may be others (kwallet?) but I haven't investiged more yet.
   I also haven't checked yet if all versions of these dependencies support
   pkg-config. The most recent versions do support it.

* configure.ac
  (SVN_APR_MAJOR_VERSION): Declare. APR's major version number is needed
   to select the correct pkg-config script name (e.g. apr-1 or apr-2).
   Generate .pc files from pc.in files.

* subversion/libsvn_auth_gnome_keyring, subversion/libsvn_auth_kwallet,
  subversion/libsvn_client, subversion/libsvn_delta, subversion/libsvn_diff,
  subversion/libsvn_fs, subversion/libsvn_fs_base, subversion/libsvn_fs_fs,
  subversion/libsvn_fs_util, subversion/libsvn_fs_x, subversion/libsvn_ra,
  subversion/libsvn_ra_local, subversion/libsvn_ra_serf,
  subversion/libsvn_ra_svn, subversion/libsvn_repos, subversion/libsvn_subr,
  subversion/libsvn_wc: Ignore generated .pc and .pc.in files.