Add -E support in executables, for use by launchers in forwarding the
environment to the user program processes when the underlying system
launcher can't do so.  The changes are:

runtime/src/arg.c
  Add -E option parsing and environment variable setting.

doc/release/README.executing
  Document the new option.

test/execflags/ferguson/help2.good
test/execflags/shannon/configs/help/basehelp.txt
test/execflags/shannon/help.good
  Update the expected "-h" output.

test/execflags/gbt/dash-E-1-opt.chpl
test/execflags/gbt/dash-E-1-opt.execopts
test/execflags/gbt/dash-E-1-opt.good
test/execflags/gbt/dash-E-1-opt.skipif
test/execflags/gbt/dash-E-2-opts.chpl
test/execflags/gbt/dash-E-2-opts.execopts
test/execflags/gbt/dash-E-2-opts.good
test/execflags/gbt/dash-E-2-opts.skipif
  New unit tests.
Merge branch 'master' of github.com:chapel-lang/chapel into dash-E
Initial support for specifying stdin file in execopts
Using execopts stdin file for knucleotide
Using execopts stdin file for reverse-complement
Adding first cut of curl support, have to fix a problem in qio_channel_revert_unlocked
Merge branch 'master' into curl
Fixing qio_channel_revert_unlocked_error. Funnily enough, the error was being caused by bad error handling in curl_preadv
changing so that clang likes it
making tiny changes
Merge branch 'master' into curl
Removing extranious inlcudes in curl plugin files
Removing superfluous includes in curl plugin files
Merge branch 'curl' of https://github.com/tzakian/chapel into curl
Renaming macro, and getting rid of two already defined macros. Fixed possible invalid
free if we failed to connect to curl. Cleaned up code in general and got rid of extra
buf writer that we didn't need.
Merge branch 'master' into curl
Ready for unit testing.
Fixing getlength in the curl plugin and change seek so that both of them work together
in qio_file_open_usr when we cannot get the length of the URL. Had to change a few
things. But, now we get good error messages when we should!
Merge branch 'master' into curl
Fixing semantics of seek, and in the process got rid of one of the fields in the
curl_handle struct. Going to add in the module code now.