Fix save and restore cursor behavior

[Tyriar]

This broke in #717.

Fixes #818

[coveralls]

Coverage increased (+0.3%) to 70.702% when pulling 604959a on Tyriar:818_fix_save_restore_cursor into f36bd24 on sourcelair:master.

[coveralls]

Coverage increased (+0.2%) to 70.567% when pulling 6ea7758 on Tyriar:818_fix_save_restore_cursor into f36bd24 on sourcelair:master.

[parisk]

ouch.

LGTM 🚀

[AndrienkoAleksandr]

Ok, merge it, but seems that's not a fix, this is alternative of real solution...

[AndrienkoAleksandr]

I am working on some tests on this topic, https://github.com/AndrienkoAleksandr/xterm.js/blob/fixFullResetTerminal/src/test/test.js#L1025
So, @Tyriar thank you for a "new testcase", I will think about how to implement some solution to cover all known testcases...

[Tyriar]

@AndrienkoAleksandr are you sure we want to save/restore the cursor when switching to/from the alt buffer? I assume it was originally commented out for a reason and I'm not sure xterm does this https://github.com/joejulian/xterm/blob/defc6dd5684a12dc8e56cb6973ef973e7a32caa3/misc.c#L4172

[Tyriar]

@AndrienkoAleksandr clarification on what's wrong with this would be good too, is it just the save/restore on buffer change?

[coveralls]

Coverage increased (+0.2%) to 70.539% when pulling ff165e8 on Tyriar:818_fix_save_restore_cursor into cdcbf60 on sourcelair:master.