Suggest ag -Q when relevant

This detects when `ag` suggests the `-Q` option, and adds it.

README.md

@@ -144,6 +144,7 @@ sudo -H pip install thefuck --upgrade
 The Fuck tries to match a rule for the previous command, creates a new command
 using the matched rule and runs it. Rules enabled by default are as follows:
 
+* `ag_literal` – adds `-Q` to `ag` when suggested;
 * `aws_cli` – fixes misspelled commands like `aws dynamdb scan`
 * `cargo` – runs `cargo build` instead of `cargo`;
 * `cargo_no_command` – fixes wrongs commands like `cargo buid`;

tests/rules/test_ag_literal.py

@@ -0,0 +1,25 @@
+import pytest
+from thefuck.rules.ag_literal import match, get_new_command
+from tests.utils import Command
+
+stderr = ('ERR: Bad regex! pcre_compile() failed at position 1: missing )\n'
+          'If you meant to search for a literal string, run ag with -Q\n')
+
+matching_command = Command(script='ag \\(', stderr=stderr)
+
+@pytest.mark.parametrize('command', [
+    matching_command])
+def test_match(command):
+    assert match(matching_command)
+
+
+@pytest.mark.parametrize('command', [
+    Command(script='ag foo', stderr='')])
+def test_not_match(command):
+    assert not match(command)
+
+
+@pytest.mark.parametrize('command, new_command', [
+    (matching_command, 'ag -Q \\(')])
+def test_get_new_command(command, new_command):
+    assert get_new_command(command) == new_command

thefuck/rules/ag_literal.py

@@ -0,0 +1,11 @@
+from thefuck.utils import for_app
+from thefuck.utils import replace_argument
+
+
+@for_app('ag')
+def match(command):
+    return 'run ag with -Q' in command.stderr
+
+
+def get_new_command(command):
+    return command.script.replace('ag', 'ag -Q', 1)