Allow multiple colons for docker image.

Review: https://reviews.apache.org/r/24916
Updates latest version number in Getting Started documentation, and updates index of documentation files to reference recently-added docs.
Adds link to Authorization doc in documentation home, and updates punctuation to be consistent.
Adds Oscar Insurance and Squarespace to PoweredByMesos page.
Fixed the build error in routing tests.

Review: https://reviews.apache.org/r/24902
Fixed MesosContainerizer to reject tasks that have ContainerInfo set.

Review: https://reviews.apache.org/r/25033
Log the uid and pid when receiving a SIGTERM.

Review: https://reviews.apache.org/r/24700
Refactored the JSON output streaming.

Review: https://reviews.apache.org/r/24877
Adjustments for new JSON streaming.

Review: https://reviews.apache.org/r/25053
Added logging when master/slaves/frameworks bind to loopback address.

Review: https://reviews.apache.org/r/25055
Fixed timed_tests.sh script to preserve exit status of the test.
Use curl-config to locate lib curl when possible

If libcurl.a is located on a non-standard path, the test for libcurl in the configure script fails, even if the path is specified in LDFLAGS.

To work around this we can use curl-config to provide the needed path and link options to the compiler.

This patch modifies configure.ac to check for curl-config and use its output as an argument to AC\_CHECK\_LIB if possible.

Review: https://reviews.apache.org/r/24407
Minor style fixes from: https://reviews.apache.org/r/24407/
Removed duplicate headers imports

Review: https://reviews.apache.org/r/25042
Replaced PKG_CHECK_MODULES with AC_CHECKs in configure.ac.

Review: https://reviews.apache.org/r/25030
Replaced PKG_CHECK_MODULES with AC_CHECKs in libprocess configure.ac.

Review: https://reviews.apache.org/r/25031
Fixed signal handling for stout.

Review: https://reviews.apache.org/r/25126
Fixed signal handling in libprocess.

Review: https://reviews.apache.org/r/25128
Fixed signal handling for Mesos.

Review: https://reviews.apache.org/r/25129
Improved the signal handling comment in Mesos tests.