Merge pull request pkg#410 from pkg/export-realpath

Export RealPath for potential client use

Merge pull request pkg#376 from pkg/update-go-mod-for-1-12

Update go.mod dependencies ahead of 1.12 release

Bugfix and small feature release.

First release in some time. Fixing lots of bugs and adds a few new
features. Below are the highlights.

Features:
* [pkgGH-301] support rename extension for server
* [pkgGH-332] Added a ClientOption to determine whether to use Fstat or Stat
* [pkgGH-315] make SFTP extensions configurable

Bugfixes:
* [pkgGH-291] Wrong S_IFMT mask when converting filemode bits to os.FileMode
* [pkgGH-295] sftp resume produces corrupted files
* [pkgGH-298] Extensions are not announced by the server
* [pkgGH-329] fix S_IFMT value on windows, plan9 and js/wasm
* [pkgGH-325] Request.Attributes() panics when called with the Attr slice empty
* [pkgGH-309] fix: received packet too long

Thanks to all the contributors. Your time and patience is appreciated.

go modules update

make client more resilient with servers that don't support full protocol

client can now detect sftp connection close

Implments a clintConn.Wait() method.
Fixes: pkg#278

Thanks @wutzx for the PR.

fixes tests to run on windows

refactor opening files/dirs in request-server

Minor version bump due to a pretty heavy refactoring of the
request-server's handing of open packets. It now calls through to the
handler to initialize the reader/writer/lister objects when it receives
the open packet. This should be transparent and was done in relation to
a bug fix, but it is a pretty major refactor so the minor version bump.

Fixed pkg#280; Request.WithContext() deadlock when called from handler

Fix race issue in request server.

Fixes issue with lock/race condition in request server get/put.

bugfix release

fixes pkg#264; issue with rename in request example
fixes pkg#265; open/stat packet race condition (fixes sshfs as client)

Bugfix release.

Fixes pkg#260; packet ordering bug with ws-ftp client
Adds gcc-go AIX support.