provider/dnsimple: Document DNSimple env vars

provider/aws: Fix issue in updating Route 53 records on refresh/read.

providers/docker: default cert_path to non-nil so input isn't asked [GH-1432]

terraform: copy RawConfigs to avoid races

terraform: don't prune, but disable, inherited configs [GH-1447]

Update CHANGELOG

Catching up with my post 0.4 CHANGELOG lag.

providers/aws: fix a few more bugs in launch configs

providers/aws: reduce scope of block_device set hashcodes

Update CHANGELOG

terraform: don't validate providers outside of modules if we don't have to

Fixes #1409

Resource set hash calculation is a bit of a devil's bargain when it
comes to optional, computed attributes.

If you omit the optional, computed attribute from the hash function,
changing it in an existing config is not properly detected.

If you include the optional, computed attribute in the hash and do not
specify a value for it in the config, then you'll end up with a
perpetual, unresolvable diff.

We'll need to think about how to get the best of both worlds, here, but
for now I'm switching us to the latter and documenting the fact that
changing these attributes requires manual `terraform taint` to apply.

These bugs were found by additional check added in #1443

 * Reversed nil err check meant that block devices were broken :(
 * Fixing the err check revealed a few missed pointer derefs
 * Unlike instances, ephemeral block devices do come back in
   `BlockDeviceMappings` from `DescribeLaunchConfigurations` calls, so
   we need to recognize them and filter them properly. Even though
   they're not set as computed, I'm doing a `d.Set` since it doesn't
   hurt and it gives us the benefit of basic drift detection.

ec2/config: Use provided region instead of hardcoding us-west-2

provider/aws: Convert AWS Network Interface to aws-sdk-go

provider/aws: Convert EIP to use upstream aws-sdk-go

Convert AWS Internet Gateway to use upstream aws-sdk-go

provider/aws: Convert AWS Subnet to mainstream aws-sdk-go