Fix "docker load" help by removing "SOURCE" prompt and mentioning STDIN

Fixes #3383
Add more TestBuild Dockerfiles, especially for making sure manual RUN echo '#!...' continues to work correctly
Cleanup: runtime.getFullName is deprecated by getFullName
Merge pull request #3384 from tianon/fix-load-help

Fix "docker load" help by removing "SOURCE" prompt and mentioning STDIN
Merge pull request #3420 from RoelVanNyen/getfullname

Cleanup: runtime.getFullName is deprecated by getFullName
Merge pull request #3388 from tianon/more-build-tests

Add more TestBuild Dockerfiles, especially for 'echo shebang' testing
Move utility package 'iptables' to pkg/iptables
Merge pull request #3328 from shykes/pkg-iptables

Move utility package 'iptables' to pkg/iptables
[docs] Fix for wrong version warning on master instead of latest.
Merge pull request #3473 from dhrp/docs-version-warning-fix

[docs] Fix for wrong version warning on master instead of latest.
Update REMOTE_TODO.md
Make CopyFileWithTar use a pipe instead of a buffer. Save more than 1Gb of ram for a 500Mb file.
Merge pull request #3477 from creack/fix_tar_leaks

Make CopyFileWithTar use a pipe instead of a buffer. Save more than 1Gb of ram for a 500Mb file.