main: drop "on-disk format" from -version output, add Go version

As v0.4 introduced ext4-style feature flags, the on-disk format version
is unlinkely to change. Drop it from the version output to reduce
clutter. Use "gocryptfs -version -debug" to see it.

Add the Go version string because only Go 1.6 and newer have an optimized
AES-GCM implementation. This will help users to understand the performance
of their build.

Documentation/MANPAGE.md

@@ -125,7 +125,10 @@ option.
 mounting but makes the password susceptible to brute-force attacks (default 16)
 
 **-version**
-:	Print version and exit
+:	Print version and exit. The output contains three fields seperated by
+";". Example: "gocryptfs v0.12-2; go-fuse a4c968c; go1.6.2".
+Field 1 is the gocryptfs version, field 2 is the version of the go-fuse
+library, field 3 is the Go version that was used to compile the binary.
 
 **-wpanic**
 :	When encountering a warning, panic and exit immediately. This is

build.bash

@@ -12,7 +12,7 @@ GITVERSIONFUSE=$(cd $GOPATH/src/github.com/hanwen/go-fuse && git rev-parse --sho
 # Make sure we have the go binary
 go version > /dev/null
 
-# go version go1.5.1 linux/amd64
+# "go version go1.6.2 linux/amd64" -> "1.6"
 V=$(go version | cut -d" " -f3 | cut -c3-5)
 
 if [ $V == "1.3" -o $V == "1.4" ]

main.go

@@ -151,8 +151,8 @@ func changePassword(args *argContainer) {
 // printVersion - print a version string like
 // "gocryptfs v0.3.1-31-g6736212-dirty; on-disk format 2"
 func printVersion() {
-	fmt.Printf("%s %s; on-disk format %d; go-fuse %s\n",
-		tlog.ProgramName, GitVersion, contentenc.CurrentVersion, GitVersionFuse)
+	fmt.Printf("%s %s; go-fuse %s; %s\n",
+		tlog.ProgramName, GitVersion, GitVersionFuse, runtime.Version())
 }
 
 func main() {
@@ -218,6 +218,7 @@ func main() {
 	// "-v"
 	if args.version {
 		tlog.Debug.Printf("openssl=%v\n", args.openssl)
+		tlog.Debug.Printf("on-disk format %d\n", contentenc.CurrentVersion)
 		printVersion()
 		os.Exit(0)
 	}