Some SAC files don't have leven set.

This is not really valid but files out in the wild do it and SAC can also read those files.
Fix NumPy loadtxt wrapper arguments.

The NumPy loadtxt keyword is called 'ndmin', not 'ndlim', so this
wrapper is used even in the new versions.
Use a non-empty array for testing np.loadtxt.

An empty array causes a warning from NumPy, and the result doesn't
really matter anyway.
Merge pull request #818 from QuLogic/fix-loadtxt-shim

Fix loadtxt shim
Added test case for a segfaulting RESP file.
Avoid segfault by declaring a variable to be volatile.

The problem was that clang (not tested with gcc) somehow messed with
local variables when using setjmp/longjump when optimization was turned
on.

The tip to turn it into a volatile variable is from here although is
does not appear to be the exactly the same problem:
http://stackoverflow.com/a/7996969
Raise a more specific error when evalresp fails to calculate a response.
Adjust test case to catch exception.
Manually check the source depth. Fixes #757.
Maximum depth actually depends on the model.

800 km works for both and should be plenty. It is non-trivial
to actually parse the model files to figure out the depth.
Merge pull request #819 from krischer/evalresp_segfaults

Remove a segfault in evalresp
Merge branch 'master' into warning-cleanup

Conflicts:
	obspy/signal/src/evalresp/evresp.c
Merge pull request #1 from krischer/warning-cleanup

Manually merging master