plumb/basic: avoid wrap around in file:1:2 (#158) Fixes #122, #140. As reported in #122, `file:1:1` moves to the end of the file, and `file:1:2` fails with “address out of range”. I’ll use file:2:3 as an example so we can tell the line and column number apart. What’s happening is this: plumb/basic matches `2:3` using twocolonaddr (from plumb/fileaddr), then sets addr to `2-#1+#3` (the 1 is constant and was introduced because column numbers are 1-based). Acme interprets this in three steps: 1. find the range (q0, q1) that contains line 2 2. create the range (q2, q2) where q2 = q0 - 1 3. create the range (q3, q3) where q3 = q2 + 3 The second step has a branch where if q0 == 0 and 1 > 0 (remember that 1 is constant and comes form plumb/basic), q0 is set to the end of the file. This makes addressing things at the end of the file easier. The problem then is that if we select line 1, which starts at the beginning of the file, q0 is always 0 and the branch in step 2) will always be used. `1:1` is interpreted as `1-#1+#1` which starts at 0, wraps around to the end of the file, then moves 1 character backwards and then forwards again, ending at the end of the file. `1:2` is interpretes as `1-#1+#2` which starts at 0, wraps around to the end od the file, then moves 1 character backwards and tries moving 2 characters forwards beyond the end of the file, resulting in the out of range error. In #140 @rsc proposed transforming `:X:Y` into `:X-#0+#Y-#1` instead since that avoids wrapping around by not moving backwards at first. This change modifies `plumb/basic` to do that.

plumb: allow @ in file names Helps Go module download cache, Upspin, maybe others.

acme: scroll a directory window when navigating if: - the cursor is on the last line - the navigation would put the cursor over the tag of the following text R=rsc CC=smckean83 https://codereview.appspot.com/15280045

plumb: character offsets start at 1, not 0 x:10:1 is the beginning of line 10 R=rsc http://codereview.appspot.com/4960049

plumb: column numbers in file address R=rsc http://codereview.appspot.com/2776042

plumb: change inferno module path to /usr/inferno/module (Anthony Sorace)

plumbing: move email rule below file rules (Bengt Kleberg)

plumb all urls, not just images (TheWhiteTiger)

allow _ - / in header file names

use 9 page instead of page

add $plan9 variable

call wmail to send mail.

plumbing foo.html now sends it to the editor -- this is more in keeping with plan 9 behavior. plumbing file:foo.html adds the appropriate full path and sends it to the web browser.

use psv

plumb urls and html to web browsers