Added fgmax option and various other fixes

Requires PR clawpack/clawutil#58.

The major change is adding an fgmax option described below.

Also added optional new setrun parameters 
  rundata.geo_data.manning_coefficient_onshore
  rundata.geo_data.friction_shore_level
to allow a different Manning coefficient to be specified onshore (where B > friction_shore_level) than offshore (where the original manning_coefficient is used).  If this is not specified, then manning_coefficient is used both onshore and offshore.  This is very useful for tsunami modeling where trees, etc. give a much larger onshore Manning coefficient.  Documented in http://clawpack.github.io/doc/setrun_geoclaw.html#setrun-geoclaw

Added new option to specified "fixed grids" on which to keep track of maximum amplitude of quantities over the entire computation.  Also keeps track of time the maximum is observed, and of the "arrival time" for tsunamis.

This is an improvement over the previous fixedgrids (which are still in place) -- it calculates properly at the intersection of patches at the same level, which the previous version did not always do.  There is also more flexibility in defining the set of points to monitor -- it can be an arbitrary list of (x,y) points and multiple files of such points can be specified, e.g. a rectangular grid, a 1d transect, or a set of points following a coastline.

On the other hand it does not output the solution at various times on the fixed grid, only keeps track of max.  

The new routines in geoclaw/src/2d/shallow are of the form fgmax_*.f90.  The file fgmax_values.f90 is where the values to be monitored are specified.  The default is currently to monitor
  eta tilde = h+B  where h>0 or = sea_level where h=0
  speed
  momentum
  momentum flux  (important for estimating forces on structures)
Monitoring eta tilde rather than eta or h turns out to be best to keep track of both onshore depth and offshore elevations, at least for tsunamis.

Two examples can be found in geoclaw/dev/bowl-slosh_fgmax and geoclaw/dev/chile2010_fgmax.  These need to be cleaned up further and moved to apps, or replaced with more interesting examples.  

Documentation is yet to come --- for now see the README.txt files in the above two directories to try running and plotting.

In particular, the example in geoclaw/dev/chile2010_fgmax should produce a plot zeta.png as shown below, with maximum amplitude in colors and contours of arrival time:

![zeta](https://f.cloud.github.com/assets/720122/1134223/ff38cd44-1bec-11e3-9c29-24a42d4c0575.png)