Don't warn about spacing around << as difficult to know if we should

Since we can't in general (without type analysis I think) tell the
difference between a bit shift operator << and a stream manipulator <<
we don't warn about it. In some instances we can tell if it is a stream
manipulator so we check for spaces there. I've added a known bug
operator-spacing3 that would be the perfect report of errors.

regression/cpp-linter/operator-spacing2/main.cpp

@@ -0,0 +1,19 @@
+/*******************************************************************\
+
+Module: Lint Examples
+
+Author: Thomas Kiley, thomas@diffblue.com
+
+\*******************************************************************/
+
+static void fun()
+{
+  status() << "Adding CPROVER library (" << eom;
+
+  int x = 1<<4;
+
+  status()<<"Adding CPROVER library ("<<eom;
+
+  // Ideally this should produce an error, see operator-spacing3
+  int x = 1 << 4;
+}

regression/cpp-linter/operator-spacing2/test.desc

@@ -0,0 +1,7 @@
+CORE
+main.cpp
+
+^main\.cpp:15:  Missing spaces around <<  \[whitespace/operators\] \[3\]
+^Total errors found: 1$
+^SIGNAL=0$
+--

regression/cpp-linter/operator-spacing3/main.cpp

@@ -0,0 +1,18 @@
+/*******************************************************************\
+
+Module: Lint Examples
+
+Author: Thomas Kiley, thomas@diffblue.com
+
+\*******************************************************************/
+
+static void fun()
+{
+  status() << "Adding CPROVER library (" << eom;
+
+  int x = 1<<4;
+
+  status()<<"Adding CPROVER library ("<<eom;
+
+  int x = 1 << 4;
+}

regression/cpp-linter/operator-spacing3/test.desc

@@ -0,0 +1,10 @@
+KNOWNBUG
+main.cpp
+
+^main\.cpp:15:  Missing spaces around <<  \[whitespace/operators\] \[3\]
+^main\.cpp:15:  Missing spaces around <<  \[whitespace/operators\] \[3\]
+^main\.cpp:17:  Remove spaces around <<  \[whitespace/operators\] \[4\]
+^main\.cpp:17:  Remove spaces around <<  \[whitespace/operators\] \[4\]
+^Total errors found: 4$
+^SIGNAL=0$
+--

scripts/cpplint.py

@@ -3464,7 +3464,7 @@ def CheckOperatorSpacing(filename, clean_lines, linenum, error):
   # Note that && is not included here.  This is because there are too
   # many false positives due to RValue references.
 #  match = Search(r'[^<>=!\s](==|!=|<=|>=|\|\|)[^<>=!\s,;\)]', line)
-  match = Search(r'[^\s](<<|&&|\|\|)[^\s]', line)
+  match = Search(r'[^\s](&&|\|\|)[^\s]', line)
   if match:
     error(filename, linenum, 'whitespace/operators', 3,
           'Missing spaces around %s' % match.group(1))