Remove trailing newlines from error strings in ihex_copy.c.

The error messages are likely to be used within another message
string, where the newlines can be very disturbing.  This also unifies
error messages between ihex_copy.c and other sources.
Remove trailing punctuation from error messages.

Being a library, the generated error messages will likely be used
within another message context (such as parentheses).  This error
message convention is in compliance with the C library's strerror()
function.
Merge pull request #11 from acolomb/errmsg-formatting

Error message formatting