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>

Don't unset things that are already set as executable for the generic path.
OS X overrides this behaviour and detects if it's an MachO executable but
there's no cross-OS generic equivalent so just fall back to whatever the build
system has set.

* global: add RUBY_TWO global variable.

* test-bot: use RUBY_TWO global variable.

* github: produce better curl error messages.

If we don't know why curl has failed then ensure that the error messages
that it produced are included as part of the user output.

Would have made it easier to debug
https://github.com/Homebrew/homebrew-core/issues/2804 where wasn't clear which
directory was causing the issue.

Vendored Ruby tweaks

Changes to our style configuration:

- Consolidate all rules related to Ruby 1.8 compatibility in one place.
- Codify our de-facto preference for `alias_method` over `alias` (drops
  offense count by 54 after turning this on).
- Drop `Style/SignalException` as `only_raise` has been the new default
  for quite a while (since RuboCop 0.37.0).

Fixes #491.

vendor ruby

* Use vendor Ruby if it's present
* Install vendor Ruby for system without Ruby 2.x