Json accept-type returns json error

Conflicts:
	pyramid/tests/test_httpexceptions.py
Json accept-type returns json error

Conflicts:
	pyramid/httpexceptions.py
moved imports

Conflicts:
	pyramid/httpexceptions.py
moved imports
added MIMEAccept accept type matching
added MIMEAccept accept type matching
retriggering travis ci
fixed issue with order of types
fixed issue with order of types
Merge branch 'feature.json-exceptions' into 1.5-branch