Adjusts cancel methods in base plugin classes to exit immediately
1127817 - return a 404 for consumer history request if consumer id does not exist
1145734 - more correct error message when apache fails
1160794 - update python-requests to 2.4.3

python-requests 2.2.1 appears to have a bug that prevents re-using the same
session when downloading SSL content via proxy. The code below will work on
2.4.3 but not 2.2.1.

```python
import requests
from urlparse import urljoin

proxy_url = "http://<proxy_hostname>:<port>"
proxies = {"http": proxy_url, "https": proxy_url}
base_url = "https://repos.fedorapeople.org/repos/pulp/pulp/demo_repos/pulp_unittest/"

s = requests.Session()
print "Attempting to retrieve two files from %s using the same session..." % base_url
print s.get(urljoin(base_url, "comps.xml"), proxies=proxies)
print s.get(urljoin(base_url, "updateinfo.xml"), proxies=proxies)
```

python-requests 2.4.3 allows Pulp to download content in these cases. Note that
not all repos with SSL enabled are affected by this.
Automatic commit of package [pulp] release [2.5.0-0.17.rc].
Automatic commit of package [pulp-nodes] release [2.5.0-0.17.rc].
add section about build tools
Merge pull request #1276 from beav/building-concepts

add section about build tools
Merge pull request #1284 from asmacdo/1127817

1127817 - return a 404 for consumer history request if consumer id does not exist
Merge branch '2.5-dev'
Merge branch 'master' of https://github.com/pulp/pulp
This is the first mention of `builder.py` for some builds and we should be clear where it is.
Move the copy paths helpers into pulp.devel.

The plugin projects could use this code too.
Merge branch 'copy_paths'
Merge pull request #1291 from asmacdo/smalladdbuilddocs

First mention of `builder.py` for some builds, we should mention location
Merge pull request #1290 from beav/requests-243

1160794 - update python-requests to 2.4.3
Automatic commit of package [python-requests] minor release [2.4.3-1].
Merge remote-tracking branch 'origin/2.5-dev'
Automatic commit of package [pulp] release [2.5.0-0.18.rc].
Automatic commit of package [pulp-nodes] release [2.5.0-0.18.rc].