Speeding up triggerOnset with deque

- will bring a big speed up, when the trigger list is very longish
- proposed by
  http://pyvideo.org/video/1780/transforming-code-into-beautiful-idiomatic-pytho
Being more pythonic, refactoring

- using else statements in for loops
- proposed by
  http://pyvideo.org/video/1780/transforming-code-into-beautiful-idiomatic-pytho
add option "prefix" (default "obspy-") for NamedTemporaryFile
Merge pull request #546 from megies/tempfile_prefix

"obspy-" prefix for temp files
Option to ignore file size check in reading sac files

Checking for consistency between actual and theoretical
file size (from `npts`) can be disabled both in
`SacIO.ReadSacFile()` and in `sac.core.readSAC()`.
This is obtained by passing the parameter: `fsize=False`.

`sac.core.isSAC()` has been rewritten, in order not to
rely on `npts` to check file format, but rather checking
`nvhdr` and `delta`, as in `SacIO.IsSACfile()`.
Testing fsize option in reading sac files

Adds test cases for core.read() and SacIO.ReadSacFile()

See also #549
Merge branch 'sac' into bleeding