cmake: Allow users to specify CMAKE_INSTALL_PREFIX

Check whether CMAKE_INSTALL_PREFIX is defined before overwriting
its value.  This allows users to specify an alternate install prefix
during the `cmake` invocation.

Signed-off-by: David Aguilar <davvid@gmail.com>
cmake: Do not hard-code the path to doxygen

Use ${DOXYGEN_EXECUTRABLE} instead of hard-coding /usr/bin/doxygen.

Signed-off-by: David Aguilar <davvid@gmail.com>
cmake: Allow out-of-tree builds

We were referring to a build directory that does not exist
when building out-of-tree.

For example:

	mkdir build
	cd build
	cmake ..
	make
	make DESTDIR=$PWD/DESTDIR install

The `install` step will fail because build/src/py/partio.py
does not exist.  Remove the src/ subdirectory in the path so
that the file beneath build/ is found.

Signed-off-by: David Aguilar <davvid@gmail.com>
Merge pull request #27 from davvid/cmake

CMake enhancements
ZIP: Fixed memory corruption when reading file header.
fixed writing of id and neighbor attributes

also removed cout statements that slow down the writing of .bin files
significantly.
fixed more issues with the bin loader: neighbor channel type is correct now, uvw channel is fixed, and bin will now load into realflow without crashing
Fix bug in python bindings when editing indexed strings
Support hclassic and bhclassic
Fixes bug where empty particle set will crash on findNPoints() and also add ptf support

Fixes Bug #25741
Fixes Bug #25742

Conflicts:
	src/lib/core/KdTree.h
	src/lib/io/ParticleIO.cpp
Updated scons scripts to put tests in tests/partio directory.

Signed-off-by: Mark McLaughlin <mark.mclaughlin@disneyanimation.com>

Conflicts:
	Makefile
	src/doc/SConscript
	src/tests/SConscript
build: tests go in share/test/partio
Fix destructor warning in python interface
fix typos in README
- fix GLUT/OpenGL include paths for the tools
- fix the build with Clang 3.3 and libcxx (LLVM)
-Fixed some incorrect assumptions about PRT files:
* Now using stored header sizes (since newer PRT versions might add fields)
* Now not assuming channels are stored contiguously in memory (using 'offset' value instead)
Merge pull request #37 from nikai3d/patch-1

fix typos in README
Merge pull request #35 from SteffenL/master

ZIP: Fixed memory corruption when reading file header
-Reverted whitespace changes