Bug #430: Use the function "list(APPEND ...)" at more places in build scripts

The command "list(APPEND ...)" can be executed more efficient than the setting
of variables as before. Specific support was added by the tool "CMake 2.4".
http://cmake.org/Wiki/CMake_Performance_Tips#Use_LIST.28APPEND_....29

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Add getRGBVector3i() to every point type with RGB

Currently only some of the point types with RGB have methods to access
their RGB data as an Eigen vector.

This commit moves definitions of `getRGBVector3i()` and
`getRGBVector4i()` inside `PCL_ADD_RGB` macro so that every point type
with RGB field gets these functions.
Split PCL_ADD_POINT4D and PCL_ADD_NORMAL4D into parts

PCL_ADD_POINT4D becomes a composite of two simpler macros:

* PCL_ADD_UNION_POINT4D
* PCL_ADD_EIGEN_MAPS_POINT4D

The former adds a union, and the latter adds a family of Eigen vector
accessors. The same holds for PCL_ADD_NORMAL4D. These splits are not
strictly necessary, as both macros are always used together. However,
this way the style consistent with PCL_ADD_..._RGB macros, which we
ought to have separated.
Split PCL_ADD_RGB macro into two parts

In some point types the RGB union is a part of a larger struct, so we
can not have Eigen vector accessors in the same macro.
Add getRGBAVector4i() and getBGRVector3/4cMap() functions
Add tests for all combinations of point types and Eigen vector accessors
Fixed segfaulting in people_detector due to uninitialized variable
added inline to function in point_types_conversions.h

the inline keyword is necessary to prevent multiple definitions errors
Merge branch 'appending_of_elements_to_CMake_lists' of git://github.com/elfring/pcl
Merge pull request #450 from taketwo/add-getrgbvectori3-to-macro

Add `getRGBVector3i()` to every point type with RGB
Merge pull request #470 from jworch/master

Fixed segfaulting in people_detector due to uninitialized variable
Merge pull request #472 from manmart/inlinefix

added inline to function in point_types_conversions.h
Update link to people data, closes #469
Remove quotes from ${Boost_SYSTEM_LIBRARY}, closes #468.