Removed panic channel, replaced by integrated logging and issue reporting
<!-- Please describe your changes on the following line: -->
Remove the previous ad hoc panic channel, replace it by an integrated logging and panicking mechanism, including crash reporting. All thread panics are now reported, not just content threads.
---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix#11838
- [X] These changes do not require tests because we don't test error reporting
<!-- Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process. -->
<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/12468)
<!-- Reviewable:end -->
Check for Resources on case sensitive filesystem
<!-- Please describe your changes on the following line: -->
Case where this is needed:
http://logs.glob.uno/?c=mozilla%23servo&s=1+Jul+2016&e=1+Jul+2016#c471192
Another option is to make the Resources folder on the mac .app bundle be lower case; however, it is standard to have `Resources` in a .app bundle.
---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [ ] These changes fix #__ (github issue number if applicable).
<!-- Either: -->
- [ ] There are tests for these changes OR
- [ ] These changes do not require tests because _____
<!-- Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process. -->
<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="35" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/12137)
<!-- Reviewable:end -->
prefs: Make the preferences be guarded by a RwLock instead of a Mutex
<!-- Please describe your changes on the following line: -->
---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
<!-- Either: -->
- [x] These changes do not require tests because internals.
<!-- Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process. -->
This should reduce unnecessary locks that happen when we read preferences.
<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="35" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/12275)
<!-- Reviewable:end -->
Add `--version` flag
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy --faster` does not report any errors
- [X] These changes fix#11241 (github issue number if applicable).
Either:
- [ ] There are tests for these changes OR
- [ ] These changes do not require tests because _____
Not 100% sure of a good way to test this, so I'm submitting as is for feedback. Manually testing it appears to work fine.
<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="35" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/11262)
<!-- Reviewable:end -->