implement DescribeAccountAttributes API call
updates for default VPC functionality, missing API calls, and misc fixes

    update EC2 API version to 2013-06-15
    add :elb import tag to match ELB documentation
    handle ELB (and future RDS) error objects properly in async_send_error()
    move *_call functions to matching REST modules so API updates affect one file
    add publicDnsName,allocationId object methods to NetworkInterface/Association.pm
    add privateDnsName object method to NetworkInterface/PrivateIpAddress.pm
    fix ConfigureHealthCheck dispatch method in elastic_load_balancer.pm
    update max iops per volume to 4000 in docs
    re-add DescribeVpcAttribute,ModifyVpcAttribute calls to vpc.pm (lost in refactor)
    add isDefault object method to VPC.pm
    add defaultForAz,mapPublicIpOnLaunch object methods to Subnet.pm
    add lib/VM/EC2/AccountAttributes.pm to MANIFEST
wait_for_terminal_state(): should only set timer if $timeout > 0; wait_for_snapshots() was broken due to $timeout=0
error XML from EC2 API calls use RequestID instead of requestId, ELB uses RequestId
more fixes to properly handle request ID for ELB
bugfixes

Instance.pm		current_status would occasionally fail -- now retry a few times
elastic_ip.pm		AllocationId typo.  AllocationId cannot be simultaneously provided with PublicIp
SecurityGroup.pm	when protocol was -1 (ALL), revoke functions thought it was an argument
Add CopyImage API call (lost in refactor?)
Small fixes for run_instances() placement arguments
Merge pull request #22 from lkinley/master

Updates/fixes