Implement test_tcl and test_tk targets.

These new targets facilitate Tcl/Tk testing.

The test_tcl target depends on all Tcl-related targets that have
nothing to do with Tk.

The test_tk target depends on the remaining Tcl/Tk targets.
Only do try_compile concerning HAVE_SAHOOKS if the information is not
cached already.

This is supposed to happen in any case according to CMake
documentation, but does not.  So for the --debug-trycompile case
(which explicitly does not clean up CMakeFiles/CMakeTmp after each
try_compile) cannot follow documentation suggestion to simply remove
from the cache the try_compile result you want to debug.  Therefore,
have to put in an explicit if statement checking the existence of the
cache value for all try_compiles to make that suggestion work.
Put quotes around locations in Tcl and Tk configured test scripts to
protect against possible blanks in those paths.
Implement additional blank-in-path protection for Tcl/Tk/Itcl/Itk
version checking logic.
Use new example location (tailored for new airwin setup) of PLplot source
code location.
Replace references to svn by appropriate references to git since
PLplot development is now done using git.
Build system fix to install shapefiles in data/ss subdirectory.

These files are required to run example 19 in the installed examples.
Define and use INSTALL_PREFIX_BUILDTOOLS variable to clarify epa_build
setup logic.
Whitespace tweak.
message tweak + LIB_TAG cleanout.

The LIB_TAG cleanout is part of a larger project to remove all mention
of the unused LIB_TAG variable from our build_system.
Additional "blank-in-path" build-system code improvements and cleanup.

Tested by Alan W. Irwin <airwin@users.sourceforge.net> on Linux
using an epa_build with full comprehensive testing.

The code cleanups consist of a major rewrite of
the pkg_config_link_flags macro (now turned into a function),
implementation of the pkg_config_file function to configure
and install the *.pc file associated with our core C library
and language bindings of that library, and LIB_TAG cleanout.
That cleanout is part of a larger project to remove all mention
of the unused LIB_TAG variable from our build_system.
Completion of LIB_TAG cleanout

Tested by Alan W. Irwin <airwin@users.sourceforge.net> on Linux
using an epa_build with full comprehensive testing.

This commit completes a larger project to remove all mention
of the unused LIB_TAG variable from our build_system.
Correct the update hook error message

Change README.git_workflow ==> README.developers, the real name of the
file where our workflow is documented.
Update conversion documentation concerning hooks, tags, and branches

Added the instructions that were used to add the update hook to the SF
repo.  Corrected an error in how branches are remotely deleted. Added
instructions for how to propagate the tags and branches on the remote
to an existing local repo.
Adopt patched version of CMake master branch ExternalProject.cmake

This file was taken from the CMake master branch (commit 2588dca),
then patched with
http://cmake.org/gitweb?p=cmake.git;a=commitdiff;h=9f49ac3d
"ExternalProject: Avoid infinite loop on file download hash mismatch".

This infinite loop fix should get into the next CMake-3.0.x release so
eventually we will no longer need to carry this file with epa_build.
But for now we do carry it as a convenience for our CMake-2.8.x users.

Tested by Alan W. Irwin on Linux with an epa_build of qt5_lite (5.3.1).
Replace epa_build of Qt5.2.1 with epa_build of Qt5.3.1

By skipping some additional modules that are not necessary for PLplot
support, got the build time down to less than 20 minutes.

Tested by Alan W. Irwin <airwin@users.sourceforge.net> on Linux by
building PLplot against this qt5_lite (5.3.1) version (using the
-DPLPLOT_USE_QT5=ON cmake option) and by checking reasonable run-time
results were obtained for all qt devices (qtwidget, bmpqt, jpgqt,
pdfqt, pngqt, ppmqt, svgqt, and tiffqt) when running the test_all_qt
target (which also runs the test_qt_example target).  These qt device
driver results that depend on Qt5 still have vertical character
alignment issues, but the uniform large (more than half a character
height) offset that was worked out to compensate for that Qt5 bug for
Qt5.2.1 still seems to work for this Qt5.3.1 case.
Fix detection of Qt5.
Update location of Qt5.3.1 tarball

Change URL from local disk location on my computer (used for
initial testing purposes) to the correct web URL.
Added missing .mod files to the list of files to be installed.
The fact that they were missing from the install step caused a problem in
at least one case.
Update files for debian 5.10.0-0.1 release