Document bracket whitespace rules & add syntax-check rule

This documents the following whitespace rules

      if(foo)   // Bad
      if (foo)  // Good

      int foo (int wizz)  // Bad
      int foo(int wizz)   // Good

      bar = foo (wizz);  // Bad
      bar = foo(wizz);   // Good

      typedef int (*foo) (int wizz);  // Bad
      typedef int (*foo)(int wizz);   // Good

      int foo( int wizz );  // Bad
      int foo(int wizz);    // Good

There is a syntax-check rule extension to validate all these rules.
Checking for 'function (...args...)' is quite difficult since it
needs to ignore valid usage with keywords like 'if (...test...)'
and while/for/switch. It must also ignore source comments and
quoted strings.

It is not possible todo this with a simple regex in the normal
syntax-check style. So a short Perl script is created instead
to analyse the source. In practice this works well enough. The
only thing it can't cope with is multi-line quoted strings of
the form

 "start of string\
more lines\
more line\
the end"

but this can and should be written as

 "start of string"
 "more lines"
 "more line"
 "the end"

with this simple change, the bracket checking script does not
have any false positives across libvirt source, provided it
is only run against .c files. It is not practical to run it
against .h files, since those use whitespace extensively to
get alignment (though this is somewhat inconsistent and could
arguably be fixed).

The only limitation is that it cannot detect a violation where
the first arg starts with a '*', eg

   foo(*wizz);

since this generates too many false positives on function
typedefs which can't be supressed efficiently.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>

docs/hacking.html.in

@@ -212,6 +212,55 @@
     </p>
 
 
+    <h2><a name="bracket_spacing">Bracket spacing</a></h2>
+
+    <p>
+      The keywords <code>if</code>, <code>for</code>, <code>while</code>,
+      and <code>switch</code> must have a single space following them
+      before the opening bracket. eg
+    </p>
+    <pre>
+      if(foo)   // Bad
+      if (foo)  // Good
+</pre>
+
+    <p>
+      Function implementations must <strong>not</strong> have any whitespace
+      between the function name and the opening bracket. eg
+    </p>
+    <pre>
+      int foo (int wizz)  // Bad
+      int foo(int wizz)   // Good
+</pre>
+
+    <p>
+      Function calls must <strong>not</strong> have any whitespace
+      between the function name and the opening bracket. eg
+    </p>
+    <pre>
+      bar = foo (wizz);  // Bad
+      bar = foo(wizz);   // Good
+</pre>
+
+    <p>
+      Function typedefs must <strong>not</strong> have any whitespace
+      between the closing bracket of the function name and opening
+      bracket of the arg list. eg
+    </p>
+    <pre>
+      typedef int (*foo) (int wizz);  // Bad
+      typedef int (*foo)(int wizz);   // Good
+</pre>
+
+    <p>
+      There must not be any whitespace immediately following any
+      opening bracket, or immediately prior to any closing bracket
+    </p>
+    <pre>
+      int foo( int wizz );  // Bad
+      int foo(int wizz);    // Good
+</pre>
+
     <h2><a name="curly_braces">Curly braces</a></h2>
 
     <p>