added a comment about ImageMagick
SH caluclation: uncommented a series of lines in compute_forces_viscoelastic.f90, which were needed for SH calculation.
Thanks to Carl Tape for pointing out the issue.
Built an EXAMPLES directory with four different examples of both simple "internal" meshes (from meshfem2D) and external meshes. Other files
remain to be sorted into formal example directories. Other minor changes are as follows:
1. specfem2D: Reset kernel gridpoints to be written, undoing a temporary change.
2. specfem2D: For the source.txt output, switch columns 1 and 3, so that col 1 is absolute time, which is consistent with the output seismograms.
3. specfem2D (calling plotpost): Plot the station locations that are actually used (x_final_receiver, z_final_receiver), not the target stations (st_xval, st_zval).
4. meshfem2D and specfem2D: Change the output file name STATIONS to STATIONS_target, since these are target stations.
5. locate_receivers: Write the file STATIONS, which lists the actual station locations that are used.
6. recompute_jacobian: Before exiting due to negative jacobian, list the index of the (first) problematic element.
7. checkgrid and plotpost: Changed vertical axis labels from Y to Z.
Changed (x,y) to (x,z) comment in interfaces files to agree with (nx,nz)
as in Par_file.
renamed DATA_to_sort to DATA_to_sort_older_examples
use a higher frequency source in the default example in order to have a better looking output (sharper wave fronts)
added an OpenDX to display mesh elements with a negative Jacobian, to help locate and fix them
replaced scotch_5.1.10b with scotch_5.1.11
added a print statement to print the list of elements that have a negative Jacobian
added a program to check the quality of an external mesh
added a stop statement in the new routine to check the quality of external meshes
renamed check_mesh_quality_Gmsh.f90 to check_quality_external_mesh.f90
now generate smaller OpenDX mesh quality files
fixed a problem with found_a_negative_jacobian (was used before it was defined when the mesh has no element with a negative Jacobian).
also now use thiner lines in Postscript display (0 setlinewidth, which draws the thinest line that can print on a given device).
added explanations about how to control the quality of an external mesh to the manual
fixed a typo
added the definition of dummy values of Qp & Qs when reading an external velocity and density model with no attenuation
added commas to some print statements to make them clearer
adds configure script capabilities; adds manual in doc/USER_MANUAL to SPECFEM2D package
updated the list of authors