Move some stuff formerly in `Library/ENV` around:
- Move `Library/ENV/$XCODE_VERSION` to `Library/Homebrew/env/super` as they are
  all superenv wrappers and all symlinks to the same version. We never needed
  the "separate shims for separate versions" functionality and it just adds
  confusion.
- Move `Library/ENV/pkgconfig` to `Library/Homebrew/env/pkgconfig` to get more
  things under `Library/Homebrew`
- Move `Library/ENV/scm` to `Library/scm` as these wrappers are not actually
  used by or related to superenv (or stdenv) in any way.

Users may have ~/.curlrc file to include options like proxies.
However, since we overwrite HOME environment variable during the build
and test, curl won't be able to find it.

This commit solves this issue by using CURL_HOME environment variable,
which will be pointed to the original HOME path.

From `curl(1)`:
> 1) curl tries to find the "home dir": It first  checks  for  the
     CURL_HOME and then the HOME environment variables. Failing that,
     it uses getpwuid() on Unix-like systems (which returns the  home
     dir  given the current user in your system). On Windows, it then
     checks for the APPDATA variable, or as a last resort the '%USER-
     PROFILE%\Application Data'.

Closes #514.

Signed-off-by: Xu Cheng <xucheng@me.com>

This makes `Tab` compatible with `BuildOptions`.

No longer needed in `super.rb` after it was moved to `os/mac`.

Looks like it was accidentally left behind (?)

In https://github.com/Homebrew/brew/commit/0d189fae57bad6c209b471eba9e0b254a2b40886
we completely removed `effective_sysroot`, which consequently left all the
`effective_sysroot`/usr/include calls pointing at `/usr/include`. This is wildly
problematic on systems where the Command Line Tools aren't installed because
`/usr/include` is not a default-created folder prior to CLT installation.

I'm unsure if `effective_sysroot` should still be mentioned in Library/Homebrew/extend/ENV/super.rb
at all. If it can be deleted, feel free to do that without waiting for me to review.

This seems to fix:
* https://github.com/Homebrew/homebrew-core/issues/2991
* https://github.com/Homebrew/homebrew-core/issues/2986
* https://github.com/Homebrew/homebrew-core/issues/2962

* test-bot: start running generic tests.

Start running the test suite in the "generic" mode i.e. a base layer for
non-OS X platforms to be able to use to ensure we don't break the generic code
for the parts of the code we've got running.

Currently this just runs the integration tests as that's the only useful suite
that's entirely passing but eventually this will be changed to run the full test
suite in generic mode.

* test_integration_cmds: fix tests on Linux.

A temporary measure before we decide whether vendor git or not.

This means linkage checks will be invoked during `brew install` and `brew audit`

Closes #470.

Signed-off-by: Xu Cheng <xucheng@me.com>

In case of download failure and retry, altering `@url` can cause side
effect like repeatedly applying `HOMEBREW_ARTIFACT_DOMAIN`.

Regex is way slower than normal String#include? and String#start_with?.
Also, we often forget to proper escape them. So avoid using them if it
is not necessary.

Closes #503.

Signed-off-by: Xu Cheng <xucheng@me.com>

If set, this environment variable instructs Homebrew to use the given URL as a
download mirror (e.g. an Artifactory instance) for bottles and binaries.

Closes #387.

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>

`.` need to be escaped, otherwise it will match any character.

Also improve code style for handling string s.

Closes #495.

Signed-off-by: Dominyk Tiller <dominyktiller@gmail.com>