TJBench: Recover from non-fatal errors if possible

TJBench: Recover from non-fatal errors if possible

Previously, -stoponwarning only had an effect on the underlying
TurboJPEG C functions, but TJBench still aborted if a non-fatal error
occurred.  This commit modifies the C version of TJBench such that it
always recovers from a non-fatal error unless -stoponwarning is
specified.  Furthermore, the benchmark stores the details of the last
non-fatal error and does not print any subsequent non-fatal error
messages unless they differ from the last one.

Due to limitations in the Java API (specifically, the fact that it
cannot communicate errors, fatal or otherwise, to the calling program
without throwing a TJException), it was only possible to make
decompression operations fully recoverable within TJBench.  With other
operations, -stoponwarning still has an effect on the underlying C
library but has no effect at the Java level.

The Java API documentation has been amended to reflect that only certain
methods are truly recoverable, regardless of the state of
TJ.FLAG_STOPONWARNING.