Create a .gitignore file for "dub init". See #364.
Output a reason when implicitly fetching packages.
Fix optional dependencies being always downloaded with the new dependency resolver. Fixes #359.
Fix DependencyResolver's unit test.
Force upgrade of branch based dependencies. Fixes #360.
Only upgrade branch dependencies when an explicit upgrade is requested.
Add a warning for dependency specifications that mismatch the version selections. Fixes #333.
Add an explanation message for exit code -9.

This is a common enough issue to warrant a little diagnostic assistance (the compiler/linker process getting KILLed by the kernel due to out-of-memory).
Fix using an invalid configuration in DependencyResolver when validating dependencies.

This was caused by the fix for #359.
Fix UpgradeOptions.printUpgradesOnly. Fixes #323.

This commit disables fetching upgrade candidates and prints a message for each upgradeable dependency instead.
Add "singleFile" as a possible --build-mode value on the help screen.