updates tomography tools to use common subroutines
renames constants_tomography.h to constants_tomography.h.in to allow out-of-source builds; small updates in tomo rules and files
updates tomography tool routines; adds MAX_STRING_LEN parameter for strings
updates configuration and m4/ scripts (fixes configuration with CUDA and intel ifort compilers)
updates smoothing tool and adds mesh geometry to values_from_mesher.h
fixes parameter output to values_from_mesher.h file for mesh geometry (avoids line breaks)
updates interpolation tool and rules.mk in src/tomography
adds difference tool to src/tomography
Textures no longer appear in function declaration when not needed
remove texture definition when not used
remove duplicated function
Protect multiline macro function definitions

unprotected macro functions are incompatible with inline "if (use_opencl) MACRO_FCT()" ...
finish removing unused textures from kernels calls
revert src/gpu/initialize_gpu.c to original state
fix compilation bugs (cudacc stricter than gccwq)
removed white spaces
Adds initilization for backward trace arrays
updates interpolation tool; removes redundant asdf helper files; adds new flush_system.f90 file; renames long function names
added see_also_README_inversion_package_list_of_things_to_do_in_the_SPECFEM3D_package.txt
updated two comments