Ensure readable errors are printed by seash, not tracebacks...

[JustinCappos]

Right now, doing a few basic things wrong in seash results in tracebacks. It would be better to catch expected errors and print nicer error messages.

For example:

Justins-MacBook-Air:seattle_demokit justincappos$ python seash.py

• You can list all available seash modules using 'show modules' command.

Enabled modules: clearinghouse, factoids, geoip, modules, variables

!> loadkeys ../abc
Traceback (most recent call last):
File "seash.py", line 267, in command_loop
File "/Users/justincappos/Downloads/seattle_demokit/seash_dictionary.py", line 2109, in command_dispatch
File "/Users/justincappos/Downloads/seattle_demokit/command_callbacks.py", line 1534, in loadkeys_keyname
File "/Users/justincappos/Downloads/seattle_demokit/rsa", line 719, in rsa_file_to_privatekey
File "/Users/justincappos/Downloads/seattle_demokit/emulfile.py", line 179, in emulated_open
File "/Users/justincappos/Downloads/seattle_demokit/emulfile.py", line 291, in init
FileNotFoundError: Cannot openfile non-existent file "../abc.privatekey" without creating it!
!>

dubdubdub@%all !> upload aksd
Traceback (most recent call last):
File "seash.py", line 267, in command_loop
File "/Users/justincappos/Downloads/seattle_demokit/seash_dictionary.py", line 2109, in command_dispatch
File "/Users/justincappos/Downloads/seattle_demokit/command_callbacks.py", line 1864, in upload_filename
IOError: [Errno 2] No such file or directory: 'aksd'
dubdubdub@%all !>

[aaaaalbert]

Proposed fix in 5b36d1f. You may try it out my branch like so,

git clone https://github.com/SeattleTestbed/seash.git -b beautify-error-messages

followed by the usual init/build steps.

Things I tested, with "NX" refering to a non-existant file:

loadpub NX
loadpub a_key

loadpriv NX
loadpriv a_key

loadkeys NX

# Next up, try loading a key pair with only one of the keys available
loadkeys only_pub
loadkeys only_priv

on %all
upload NX
run NX