Optimizations and performance improvements

A new configuration feature is added: Feature.THRESHOLD_FOR_HOTSPOT_BYTE_CODE. The value is an integer, and indicates how often a fragment of code must be executed before it becomes a candidate for bytecode generation. The value can also be specified in a configuration file. The default is 100.

Bytecode generation now takes place (in Saxon-EE) for stylesheets reloaded from a SEF file.

A new optimization flag "t" has been added for tail-call optimization. So, for example, -opt:-t on the command line suppresses optimization of tail calls. This can be useful when debugging, as it makes the flow of control easier to understand, and ensures that all active templates and functions are visible in a stack trace. Previously some uses of tail call optimization (but not all) could be suppressed using the "m" (miscellaneous) flag.