WP 34S and 31S bugs and fixes

[Bit]

This thread can be used to discuss those bugs found in, and fixes proposed for, the WP 34S and 31S that don't warrant having their own dedicated thread.

The first ones:

1. When tracing is enabled (flag T) on the 34S emulator or the infrared-enabled build, the backspace operation is turned into CLx because print_trace() calls process_cmdline(). This means you cannot delete individual digits you just typed.

2. On the 34S if you attempt to perform an operation with a partially entered fraction in the command line, you get an error message as expected, but the same error is set again when xeq() tries to recover and calls process_cmdline_set_lift() in the "if (Error != ERR_NONE)" code branch.

Here's how to reproduce the problem:
[1] [.] [2] [.] [+]
You get an error as expected, but if you clear the error and continue with another operation:
[EXIT] [+]
Then you get another bogus error.

I've committed two patches to SVN but I'd prefer if someone else reviewed them, too.