Raise minimum Vibe.d requirement to v0.9.0 ...

Make sure a recent enough Vibe.d is used so we can update the vibecompat code.
Additionally, since the split of Vibe.d into package, and the splitting of
vibe-core into its own project, the version specification was never triggered,
so it was corrected in this commit (the version spec was correct for older Vibe.d).

Renaming a file ...

to conform to other file names.

Merge pull request #2064 from drug007/issue2051-final-fix ...

Hotfix for #2051
merged-on-behalf-of: Nicholas Wilson <thewilsonator@users.noreply.github.com>

Disable warning that import path list is empty in single file package mode

Add failing unit test in the single file package ...

to check if unit tests from the main source file run at all. Because by default the main source file is excluded from tests.

Test if dub test works with single file package with dependency

Check command execution status ...

no string processing to evaluate the result

Add comments

Add the main source file directory to import paths ...

else dub doesn't find it because the single file package do not have the default package directory structure

In single file packages the main source file shouldn't be ignored ...

because it represents all package by definition

Propagate the `single` option ...

before GeneratorSettings ignored this option

Set cwd on spawn functions instead of chdir ...

It is more hygienic to use the cwd argument as it doesn't impact
the running process, and doesn't decouple the reason for it.

Remove redundant code with relativeTo ...

The versioned code was doing almost the same thing as relativeTo,
but adding `./` or equivalent so it could be run from the cwd.
Instead of doing this complicated patching, just use the absolute
path for running, but the relative path when issuing messages to the user.

Merge pull request #2063 from Geod24/cleanup ...

Minor code cleanup (whitespace, import)
merged-on-behalf-of: Petar Kirov <PetarKirov@users.noreply.github.com>

Merge pull request #2061 from MartinNowak/merge_stable ...

merge stable
merged-on-behalf-of: Petar Kirov <PetarKirov@users.noreply.github.com>

Merge remote-tracking branch 'upstream/stable' into merge_stable

Trivial: Clean up trailing whitespace

Trivial: Remove redundant import ...

This is already imported at module scope.

Merge remote-tracking branch 'upstream/master' into stable

Add ability to specify version specification for commandline commands ...

As mentioned in the changelog, it was not possible with all commands.
No breaking changes are expected.

Normalize line endings & UTF8 BOMs

Merge pull request #2040 from omerfirmak/agora-1327 ...

Allow custom dflags to be defined for dependencies

Don't export DFLAGS & LFLAGS to nested invocations by default

Recursively apply dependencyBuildSettings ...

For now, only "dflags" is used

improve list command

Improved ldc cross compile: ...

The folder `.dub/obj` has been moved to `.dub/build-*/obj` for an independent cross / parallel build process.
Now it is possible that two processes can build the same project with different configurations.

Fix #2051 "Running unittests from dub single file packages fails" (#2052) ...

Performing test command dub imports every source file as module to build the project excluding the main source file. But this excluding may fail and in this case dub try to import the main source file as module. Single file package building fails because the main source file does not belong to any import path. Now both the current file and the main source file paths are compared in relative form to prevent importing the main source file as module.

Use DC env variable as the default compiler

Add support for --arch=x86_mscoff for LDC (for DMD compatibility)

Use compiler version, not frontend version for build IDs and paths ...

This prevents artifacts from being reused after upgrading the compiler
from a beta to a final or to a newer patch release.