TBR: i#1729 offline traces: add headers and footers

Commit log for first patchset:
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i#1729 offline traces: add headers and footers

Adds a header and footer type to each of the offline raw and finished trace
file formats.

Adds a version field to the headers to facilitate changing
the format in the future.

Uses the footer to ensure that files are not truncated by changing the
readers to look for the footer rather than just EOF and to complain on EOF.

Changes the analyzer to seek ahead and look for the footer on an existing
finished trace file to ensure we re-run drraw2trace if an earlier run was
interrupted, ran out of disk space, or whatnot: we only use a file already
present if it has a footer.

Adds a mechanism to skip the max size check when writing the footer to
ensure each thread has a footer.
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[bruening, 2016-11-11 06:22:09]

Committed as
https://github.com/DynamoRIO/dynamorio/commit/9bed8755277b6afd9992b90a8e3c2c7...

Final commit log: 
---------------
i#1729 offline traces: add headers and footers

Adds a header and footer type to each of the offline raw and finished trace
file formats.

Adds a version field to the headers to facilitate changing
the format in the future.

Uses the footer to ensure that files are not truncated by changing the
readers to look for the footer rather than just EOF and to complain on EOF.

Changes the analyzer to seek ahead and look for the footer on an existing
finished trace file to ensure we re-run drraw2trace if an earlier run was
interrupted, ran out of disk space, or whatnot: we only use a file already
present if it has a footer.

Adds a mechanism to skip the max size check when writing the footer to
ensure each thread has a footer.

Review-URL: https://codereview.appspot.com/317920043
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