Fix potential undefined index on request submission

When submitting a request for an account without a `HTTP_USER_AGENT`, a
`NOTICE` is emitted:

    Notice: Undefined index: HTTP_USER_AGENT in /var/www/includes/request.php on line 634

This patch changes the submit function to check for existence of the
`HTTP_USER_AGENT` header before adding it to the database.
Fix CheckUsers being unable to ban unless they are also tool admins.
Fixup pullreq

We want to set the useragent field in the database to a value which is
clearly unset - not a string value of "NULL".
The section above is done differently to the implementation suggested.
Merge branch 'koentje_fix_undefined_index'
rm badpass log entries - no longer exist in database.
#122 -dnsbl, -blacklist hit
fix ban reasons script
gitignore desktop.ini
Merge branch 'master' of github.com:enwikipedia-acc/waca
fix
rework the rename log into something more machine-parsable.
Use new rename log format
fixup 710f36c
Icons and spacing on navbar
Fix #116
tweak top bar layout
remove blacklist file
fix because windows is broken

woo for case-insensitive filesystems.
pdo/smartify request listing nicely.
turn off emulated prepares