Force 8 byte alignment on all platforms

Fixes bus error / unaligned access problem on RISC architectures.
[gcc-warning-fix][int-to-pointer-cast]

Please check if the includes for intptr_t are correct; I stole them from
AdvApp2Var_SysBase.hxx.
0024912: Remove unused Graphic3d_Strips
Remove generated files
[cmake-warning-fix][cmake-3.0-policy-CMP0043]

CMake 3.0 introduced policy CMP0043 which ignores the use of
COMPILE_DEFINITIONS_ suffixed variables, set policy behavior to OLD for
compatibility with version >3.0.
[cmake-warning-fix][cmake-3.0-policy-CMP0042]
Merge pull request #500 from tpaviot/review/force-8byte-alignment

Force 8 byte alignment on all platforms
Merge pull request #501 from tpaviot/review/travis-warning-fixes

Fix warnings that show up on Travis builds
Adding missing includes
Added FindOpenCL.cmake from https://gitorious.org/findopencl project
Added OpenCL support
[issue-425] Use WORDS_BIGENDIAN for DO_INVERSE

See #425.
Merge pull request #508 from tpaviot/review/cmake-policy-0043-fix

Fix CMake 3.0 warning about policy CMP0043
Merge pull request #511 from tpaviot/review/missing-include

Adding missing includes
Merge pull request #505 from tpaviot/review/opencl-support

Adding missing OpenCL support
CMake: minimize the amount of include directories

When the OCE source directory has a long path, building with MSVC fails
because the Windows command length limit is exceded by some modules.

This fixes the issue by setting include directories per-target, and not
adding include directories of dependencies if OCE_COPY_HEADERS_BUILD is
enabled. (only available when using cmake 2.8.8 or greater)
Improve travis build matrix

We want to:
 1. Build and run tests with gcc and clang
 2. Check that any combination of OCE_USE_PCH and OCE_COPY_HEADERS_BUILD builds fine

Always build with -j4.  Travis VMs are configured as 32 core machines,
but according to
  https://travis-ci.com/plans#faq
each build has at most 2 cores with 3GB of memory.  Sometimes builds failed
with -j32, they probably ran out of memory.
Add samples/ directory from OCCT 6.7.1

Subdirectory samples/mfc has been dropped, it is quite large.
Let TOOLKIT target depends on copy_${TOOLKIT}_headers

This fixes random build failures when OCE_USE_PCH=ON and
OCE_COPY_HEADERS_BUILD=ON.

When using precompiled headers with gcc, header files must be
copied before generating precompiled headers.
Build with -j8 instead of -4

See discussion in #514.