fix mkshort unique (#1168)

fix mkshort unique (#1168)

* fix mkshort unique.

1. we were off by one when deciding if we could just concatentate
the generated suffix to the name, failing to use the last available
character.
2. when attempting to copy the generated suffix to a presumably
shortened name, and the generated suffix was longer than the name,
the target of the copy was outside the name buffer.  In the common
case that the rank of size_t was greater than the rank of int, the
target was well beyond the end of name, not before as one would expect
with signed arithmetic.

With the new algorithm when the target length is insufficient to
fit both the name and the suffix we will only truncate the name as
required to fit the truncated name and the complete suffix in the
target length(as opposed to the original length of the name).
We fatal if this is not possible.

Add a test case to exercise the make unique code.

* fix reference mode.

* add notes for future enhancements

* fix testcase cut and paste booboo

* refactor mkshort input from char* to QByteArray.