Add "minsrc" target to build tarball

This adds a new target that will build the "minsrc" tarball.

It can be created on any platform now, either from the command
line or from within the Window's and Mac's project files.

The output tarball will be in the build directory.

And it's very easy to update the list of files/directories to
exclude...see scripts/CMakeLists.txt

scripts/CMakeLists.txt

@@ -0,0 +1,56 @@
+
+set( TARGET minsrc )
+set( TARGET_ROOT ${topdir} )
+
+message( STATUS "========== Configuring ${TARGET} ==========" )
+
+def_vars()
+
+# Add regular expressions of files/directories to exclude from the tarball
+#
+# NOTE: Each item will be wrapped with "^" and ".*$"
+list( APPEND EXCLUDES
+   .git
+   .gitattributes
+   .gitignore
+   lib-src/expat
+   lib-src/libid3tag
+   lib-src/libmad
+   lib-src/libogg
+   lib-src/libscorealign
+   lib-src/portaudio-v19/bindings
+   lib-src/portaudio-v19/doc
+   lib-src/portaudio-v19/testcvs
+   lib-src/portmidi/pm_csharp
+   lib-src/portmidi/pm_dylib
+   lib-src/portmidi/pm_java
+   lib-src/portmidi/pm_mingw
+   lib-src/portmidi/pm_python
+   lib-src/portmidi/pm_qt
+   lib-src/portmidi/pm_test
+   lib-src/portmidi/portmidi_cdt.zip
+   lib-src/soundtouch
+   lib-src/libvorbis
+   mac
+   plug-ins/analyze.ny
+   plug-ins/fadein.ny
+   plug-ins/fadeout.ny
+   plug-ins/undcbias.ny
+   qa
+   scripts
+   tests/ProjectCheckTests
+   todo.txt
+   win
+)
+
+set( TARBALL "${PROJECT_BINARY_DIR}/audacity-minsrc-${AUDACITY_DIST_VERSION}${AUDACITY_SUFFIX}.tar.xz" )
+   
+add_custom_target( ${TARGET}
+   COMMAND
+      ${CMAKE_COMMAND} -D GIT_EXECUTABLE="${GIT_EXECUTABLE}"
+                       -D TARGET_ROOT="${TARGET_ROOT}"
+                       -D EXCLUDES="${EXCLUDES}"
+                       -D TARBALL="${TARBALL}"
+                       -P "${_SRCDIR}/maketarball.cmake"
+)
+