protocol: add support for cross-interface enum attributes

The enum attribute, for which scanner support was introduced in
1771299, can be used to link message arguments to <enum>s. However,
some arguments refer to <enum>s in a different <interface>.

This adds scanner support for referring to an <enum> in a different
<interface> using dot notation. It also sets the attributes in this
style in the wayland XML protocol (wl_shm_pool::create_buffer::format
to wl_shm::format, and wl_surface::set_buffer_transform::transform to
wl_output::transform), and updates the documentation XSL so that this
new style is supported.

Changes since v2:
 - add object:: prefix for all enumerations in the documentation
 - fix whitespace in scanner.c
 - minor code fixup to return early and avoid casts in scanner.c

Changes since v1:
 - several implementation bugs fixed

Signed-off-by: Auke Booij <auke@tulcod.com>
Reviewed-by: Nils Christopher Brause <nilschrbrause@googlemail.com>
Reviewed-by: Bill Spitzak <spitzak@gmail.com>
[Pekka: rebased across cde251a124]
[Pekka: wrap lines and space fixes in scanner.c]
Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>

doc/publican/protocol-to-docbook.xsl

@@ -152,9 +152,22 @@
     <term><xsl:value-of select="@name"/></term>
     <listitem>
         <simpara>
-          <link linkend="protocol-spec-{../../@name}-enum-{@enum}">
-            <xsl:value-of select="../../@name"/>::<xsl:value-of select="@enum"/>
-          </link>
+          <xsl:choose>
+            <xsl:when test="contains(@enum, '.')">
+              <link linkend="protocol-spec-{substring-before(@enum, '.')}-enum-{substring-after(@enum, '.')}">
+                <xsl:value-of select="substring-before(@enum, '.')"/>
+                <xsl:text>::</xsl:text>
+                <xsl:value-of select="substring-after(@enum, '.')"/>
+              </link>
+            </xsl:when>
+            <xsl:otherwise>
+              <link linkend="protocol-spec-{../../@name}-enum-{@enum}">
+                <xsl:value-of select="../../@name"/>
+                <xsl:text>::</xsl:text>
+                <xsl:value-of select="@enum"/>
+              </link>
+            </xsl:otherwise>
+          </xsl:choose>
           (<xsl:value-of select="@type"/>)
           <xsl:if test="@summary" >
             - <xsl:value-of select="@summary"/>