add note for alternate download method in case curl fails
Updating SvnDriver trunk revision check

Not checking revision of composer.json, but from its parent directory.

See composer/composer#2849
Merge pull request #2921 from schmkr/svn-driver-patch

Updating SvnDriver trunk revision check
Merge pull request #2918 from Evan-R/patch-1

add note for alternate download method in case curl fails
Only check phar validity if phar.readonly is false