Sketch out -e flag to exec test in current shell

A key problem with this implementation is that while the setup/teardown does
run, the program will exit with 0, always (because it exits with the status of
the ts_report command, which does not know what the status is of the pipeline
before it).  Moreover, it only works for ./test and not for ts test invocation.
Make -e exit with exit status of test
Guard against usage of `ts -e`
Always keep stdout with -e

The idea being that this is as close to just running the function as possible.
Update documentation with notes on -e
Merge branch 'exec'
Fix minor issues in -h output
Fix failing test

Line number changed after merge - hadn't checked until now.
Stop testing csh as it cannot be supported

Unfortunately csh does not support the definition of functions, meaning ts
cannot be run in csh unless it is re-written as individual scripts... and maybe
not even then.