lang/rust: update to 1.29.2

[jbeich]

Summary

According to upstream diff it carries some stability fixes. Also, libgit2-sys no longer uses cmake to build.

IMPORTANT: In RC phase, waiting for release

NOTE: Candidate for MFH to 2018Q4

Test Plan

• poudriere bulk -t is green on 10.4 i386/amd64, 11.2 i386/amd64, 12.0 i386/amd64
• poudriere bulk -t is green for DEFAULT_VERSIONS+=ssl=libressl-devel and `DEFAULT_VERSIONS+=ssl=openssl
• poudriere bulk -t is green for all consumers on 11.2 i386

[tobik]

Feel free to commit once it's released.

Given that this release fixes some possible miscompilations, should we bump the revision of all consumers again to force rebuilds just in case?

[jbeich]

I've pushed "commit" button before checking RC1 matches the release. Fortunately, it does. ;)