Split out SVN_REV from SNAPSHOT define. This is to support `win-versioninfo',

but since Simon's made the corresponding change to the build process, this bit
needs checking in now (it should be harmless).

(The documentation in Recipe is slightly out of date; with luck I'll be
checking in `win-versioninfo' changes soon, and I can't be bothered to
disentangle the relevant changes in the meantime.)

[originally from svn r6367]

version.c

@@ -7,8 +7,16 @@
 
 #if defined SNAPSHOT
 
-char ver[] = "Development snapshot " STR(SNAPSHOT);
-char sshver[] = "PuTTY-Snapshot-" STR(SNAPSHOT);
+#if defined SVN_REV
+#define SNAPSHOT_TEXT STR(SNAPSHOT) ":r" STR(SVN_REV)
+#else
+#define SNAPSHOT_TEXT STR(SNAPSHOT)
+#endif
+
+char ver[] = "Development snapshot " SNAPSHOT_TEXT;
+char sshver[] = "PuTTY-Snapshot-" SNAPSHOT_TEXT;
+
+#undef SNAPSHOT_TEXT
 
 #elif defined RELEASE