Unescape escaped filter characters in #to_ber

[jzinn]

When searching for attribute values that contain asterisks or backslashes, the search results are empty when they should not be.

For example I have an Active Directory group with cn value of special*group. A search with filter Net::LDAP::Filter.begins(:cn, "special*g") should find this group, but doesn't.

I compared Wireshark captures of this query with one using the ldapsearch command line tool. The bytes sent on the wire by ldapsearch ... '(cn=special\2Ag*)', have a single 0x2a byte (the hex value of the asterisk character) between special and g, whereas the net-ldap gem sends three bytes, one for \, one for 2, and one for A.

This pull request uses the unescape method to make the net-ldap gem behave like ldapsearch, and causes my search to return the expected results. However, I wonder if the net-ldap gem doesn't already work this way to prevent existing client code from breaking due to unexpected unescaping. If so, what workaround would solve my problem?

When the unescape method was introduced, the #to_ber method was updated to use unescape in some places. This pull request updates #to_ber to use unescape a few more times. I'm curious if there is a reason the previous commit decided not to use unescape where this pull request adds it.