fix bad comparison in shell code, when Module.load is not present but Module.read is
[tracing] Initial tracing API.

This is used in conjunction with a collection & analysis server
to analyze memory usage and other aspects of a program running
under emscripten.
[tracing] Integrate the tracing stuff.
[tracing] Instrument dlmalloc.c

These changes compile out entirely if tracing is not enabled.
[trace] Point to the server's git repository.
Merge pull request #2622 from waywardmonkeys/trace

Initial tracing API (initially does memory profiling and analysis)
add glob, globfree in musl; 1.23.3
Add support for all possible 7-bit ascii characters in filenames for --preload-file, notably ', " and @.
Document the valid character set for packaging files. Fix minor syntax in example for better form.