Increase the memory for the local testing VM

[ci skip]
Add functions to get error list windows
Display errors only if no error list is visible
[Fix #468] Restore mouse support in error list

Turn cells into buttons that can be clicked.
Rebuild Texinfo manual

[ci skip]
Fix error list test cases

Regression from 5441d3d
Use proper level name in default message
Remove workarounds for D Mode issue

See https://github.com/Emacs-D-Mode-Maintainers/Emacs-D-Mode/issues/23
[Fix #471] Use source-inplace for less
Fix some docstrings
Use while loop over -any?
Drop redundant flycheck-sort-errors
Make level required for flycheck-has-errors-p
Add functions to check maximum error level
Streamline :next-checkers

Instead of mucking about with custom predicate symbols, just specify the
maximum permissible error level.
Merge pull request #472 from flycheck/refactor-next-checker

Streamline :next-checker predicates
Bump version [#472]

Announce a breaking API change
Fix doc building [#472]

Regression from 1f9c17f
Update changelog and Texinfo manual
Error on byte compiler warnings on Travis CI

Our code must be free of warnings.