Don't fail out if the python docstring on the first line of a file is…

… too long

Summary: See https://app.asana.com/0/27216215224639/40389455104495

Test Plan:
In webapp:

    python -c "print '\"\"\"' + '.' * 80 + '\"\"\"\n'" > foo.py
    ~/khan/devtools/khan-linter/runlint.py foo.py

And see that it outputs this:

    foo.py:1:80: E501 line too long (86 characters)

Instead of this:

    local variable 'linenum' referenced before assignment

Reviewers: csilvers

Reviewed By: csilvers

Subscribers: colin

Differential Revision: https://phabricator.khanacademy.org/D19293

.arcconfig

@@ -0,0 +1,5 @@
+{
+    "project_id": "khan-linter",
+    "conduit_uri": "https://phabricator.khanacademy.org/",
+    "lint.engine": "ArcanistConfigurationDrivenLintEngine"
+}

.arclint

@@ -0,0 +1,9 @@
+{
+  "linters": {
+    "khan-linter": {
+      "type": "script-and-regex",
+      "script-and-regex.script": "~\/khan\/devtools\/khan-linter\/runlint.py --always-exit-0 --blacklist=yes --propose-arc-fixes",
+      "script-and-regex.regex": "\/^((?P<file>[^:]*):(?P<line>\\d+):((?P<char>\\d+):)? (?P<name>((?P<error>E)|(?P<warning>W))\\S+) (?P<message>[^\\x00]*)(\\x00(?P<original>[^\\x00]*)\\x00(?P<replacement>[^\\x00]*)\\x00)?)|(?P<ignore>SKIPPING.*)$\/m"
+    }
+  }
+}

linters.py

@@ -131,8 +131,10 @@ def _process_one_line(self, output_line, contents_lines):
         # should work well enough.
         if ('E501 line too long' in lintline and
             bad_line.lstrip().startswith('"') and
-            bad_line.rstrip(',\n').endswith('"')):
-            for linenum in xrange(bad_linenum - 1, 0, -1):
+            bad_line.rstrip(',\n').endswith('"') and
+            bad_linenum):
+
+            for linenum in xrange(bad_linenum, 0, -1):
                 if (contents_lines[linenum].lstrip().startswith('"""') or
                     contents_lines[linenum].lstrip().startswith("'''")):
                     break