updated khmer.file error messages
handle missing input files
Merge pull request #484 from ged-lab/fix/assemstats3-nofile

handle missing input files for sandbox/assemstats3.py
update doc/install.txt to use python2 explicitly
further modifications for python2 install
Merge remote-tracking branch 'origin' into cleanup/filepy

Conflicts:
	ChangeLog
updated khmer ref & copyright year
updated commands vice @mr-c
fixed copyright year
Merge pull request #485 from ged-lab/update/use-python2

Be explicit about python2/pip2 in the install docs.
Merge pull request #483 from ged-lab/cleanup/filepy

some cleanup of file.py error messages & other minor updates.
updated reservoir sampling script to produce multiple subsamples with -S; added docs
add epilog to sample-reads-randomly.py
updated ChangeLog for multiple subsamples with sample-reads-randomly
updated epilog docstring per @mr-c
removed SHELL setting in Makefile
added long-form options; fixed epilog crashing bug by adding metavar
pep8
include script in documentation
100% coverage