Fix compiling on VS2012.

1. uint -> unsigned int
2. PCL_EXPORTS for getGlasbeyColor and getRandomColor 
3. workaround LNK2001(http://msdn.microsoft.com/en-us/library/f6xx1b1z.aspx) for GLASBEY_LUT_SIZE. Actually, "extern const" should make it have external linkage, but it doesn't work... (I guess it's a bug of VS2012).