Test for CURLSSH_AUTH_AGENT

CURLSSH_AUTH_AGENT is introduced in curl 7.28. Ubuntu 12.10 comes with
curl 7.27. If not defined we use CURLSSH_AUTH_PUBLICKEY instead.
Add curl debug function

Record curl debug information. The information is printed in case a download
results in a non HTTP related error. Usefull to debug protocols with authentication.
Manifest feature cleanup
Updated AUTHORS file
Added 'show --buildfile' to options list
manifest: Added description and license support

Added description and license to plain text manifest
Fixed deadlocks
Minor cleanup
manifest: Replaced tabs with spaces
manifest: Increased column widths
Merge branch 'download-debug'
Updated AUTHORS
Updated ChangeLog
Updated config.guess file
Updated ChangeLog
Updated ChangeLog
Merge branch 'master' of github.com:buildgear/buildgear