{LDAP,LDIF}.pod: update documentation of raw => REGEX

Do neither refer to Perl 5.8 nor to "earlier versions" of perl-ldap.
RT#93945: Util.pm: make sure $dec is defined

...before using it in a concatenation.

Thanks to Sörös József <soros.jozsef@multip.hu> for reporting the bug.
Util.pm: fix corner cases in time conversion functions

In the last second before the epoch, generalizedTime_to_time() and
time_to_generalizedTime() mis-calculated the time by ignoring the sign.
t/08time.t: tests for Net::LDAP::Util's time functions
Control/ProxyAuth.pm: fix initialization using value => ...
RT#94047: Control.pm: add missing word in POD

Thanks to Daniel Lintott <daniel@serverb.co.uk> for the bug report & patch.
tests: set default OpenLDAP DB type to mdb

Use mdb as DB type instead of bdb, because
a) mdb is now mature enough
b) bdb/hdc are slowly being phased out.
LDIF.pm: when reading, allow control values to be absent

This should fix the case for controls without values.
For controls with values, correctly strip leadin space.
LDIF.pm: if LWP is available, support the URL types it supports
META.json: "suggest" LWP for extended LDIF URL support
Makefile.PL: add "Extended URL support" based on LWP
add tests for LWP-based URLs in LDIFs
LDIF.pod: document support for LWP's URL types