introduce CHANNELLEN and convert some strncpy + \0 into strlcpy()

[michaelortmann]

Found by: michaelortmann
Patch by: michaelortmann
Fixes: enhancement only patch

One-line summary:
introduce CHANNELLEN and convert some strncpy + \0 into strlcpy()

Additional description (if needed):
we had some irc discussion about #3 and #38, this patch here should be fine as is.

Test cases demonstrating functionality (if applicable):

test case 1 (actually here are 2 places checked at once):
i startet eggdrop, invited it to a +i channel and it worked fine.
i also put 2 debug printf()s into source for test only and got:
DEBUG: sizeof last_invchan = 81
and
DEBUG: sizeof chan->name = 81
(the first DEBUG is for the invite, the second for the join)

test case 2:
.+chan #test
worked fine
i also put a debug printf() into source for test only and got:
DEBUG: sizeof chan->dname = 81

test case 3:
.+chan #test2
.tcl addchanrec -HQ #test2
Tcl: 1
i also put a debug printf() into source for test only and got:
DEBUG: sizeof ch->channel = 81

test case 4:
.dcc list
[02:46:06] #-HQ# dccstat
[...]
1 0.0.0.0 0 -HQ chat flags: cptEp/0
[..]
.tcl console 1 #test mkcoblxs
Tcl: {#test} mkcoblxs
i did .dcc list to find out idx = 1 parameter for the following .tcl console
i also put a debug printf() into source for test only and got:
DEBUG: sizeof dcc[i].u.chat->con_chan = 81

test case 5:
.stick
i also put a debug printf() into source for test only and got:
DEBUG: sizeof chname = 81

[Cizzle]

LGTM, though there's still a lot more places with the hardcoded 81.

[michaelortmann]

i did some more places.
enough for now.
because i fear, if i did even more, this pull request would become too bloated to be merged.

[Cizzle]

LGTM

[vanosg]

build

[michaelortmann]

@Cizzle: requested changes were done.

[vanosg]

build