acme: fix buffer overflow introduced in parsetag refactor

acme: allow spaces in window names There are many things we could do to make this work. an environment variable to control the character. Another option would be to use U+00A0 (non-breaking space), which renders the same as space. This change avoids changing the separator character and instead assumes that if the left side of the tag already ends in " Del Snarf |" then what comes before that is the file name. Acme already aggressively preserves the "Del Snarf |", so this should work decently well as a stop-gap. We can always try something else later. Fixes #26. Fixes #104. Fixes #329.

acme: factor out tag parsing code

acme: accept expanded URLs in look Just as look expands a click in /etc/passwd to the full name (provided that file exists), it now expands a click in https://9fans.net/ to the full URL (provided the prefix is http:// or https://). Probably more adjustment is needed.

acme: check file content before declaring file "modified since last read" Bad remote file systems can change mtime unexpectedly, and then there is the problem that git rebase and similar operations like to change the files and then change them back, modifying the mtimes but not the content. Avoid spurious Put errors on both of those by checking file content. (False positive "modified since last read" make the real ones difficult to notice.)

acme: add log file in acme root directory Reading /mnt/acme/log reports a log of window create, put, and delete events, as they happen. It blocks until the next event is available. Example log output: 8 new /Users/rsc/foo.go 8 put /Users/rsc/foo.go 8 del /Users/rsc/foo.go This lets acme-aware programs react to file writes, for example compiling code, running a test, or updating an import block. TBR=r R=r https://codereview.appspot.com/89560044

acme: claim input focus earlier R=rsc CC=plan9port.codebot http://codereview.appspot.com/5505091

acme: allow :?regexp for backward search Fixes issue 80. R=rsc http://codereview.appspot.com/4662088

acme: correct modified message after initial load; more detail in message http://codereview.appspot.com/123051

acme: sync against Plan 9, remove -$ option

acme: add -m option and avoid looking in the mirror

merge

various memory errors in acme

reopen plumber, build mail

No more unrooted paths.