auto-time stepping in SPECFEM3D_GLOBE: fix auto_NER() in GLOBE when a single chunk is used and has a size of less than 90 x 90 degrees

[komatits]

fix auto_NER() in GLOBE when a single chunk is used and has a size of less than 90 x 90 degrees; in that case, that (relatively old) routine written by Brian Savage around 2006/2007 is called, and I noticed that it makes the code blow up in most cases because the mesh it creates and/or the time step that it automatically selects is not right (probably because the mesh has changed significantly since Brian wrote that routine)

probably not urgent (in our group at least we almost always use the full Earth or else a chunk of size 90 x 90 degrees); but if other users change that the current code will likely blow up

[komatits]

Fixed by Daniel Peter:

Subject: Re: [specfem3d_globe] updates auto_time_stepping estimation of DT to account for reference 1D model and NGLL setting (28a0058)
Date: Fri, 31 Jul 2015 08:29:46 -0700
From: daniel peter

this update addresses issue #29, but still needs to be verified and tested with different setups to see if it solves the issue ...