lockfile: Support \-delimited file names in lockfile_name().

Currently paths that have only forward slashes like the following
"C:/package/binaries/conf.db" work seamlessly.

If we try the native windows filepaths i.e. "C:\package\binaries\conf.db" we
will hit the following problem:
2015-03-31T15:54:17Z|00001|lockfile|WARN|.c:\package\binaries\conf.db.~lock~:
failed to open lock file: Invalid argument

2015-03-31T15:54:17Z|00002|lockfile|WARN|.c:\package\binaries\conf.db.~lock~:
failed to lock file: Invalid argument
ovsdb-server: I/O error: c:\package\binaries\conf.db: failed to lock lockfile
(Invalid argument)

In this patch we update the lockfile_name function to also look for
backslashes, and also accommodate if we have a mix of backslashes and forward
slashes.

Signed-off-by: Alin Gabriel Serdean <aserdean@cloudbasesolutions.com>
[blp@nicira.com simplified the code]
Signed-off-by: Ben Pfaff <blp@nicira.com>

lib/lockfile.c

@@ -82,6 +82,14 @@ lockfile_name(const char *filename_)
      * symlink, not one for each. */
     filename = follow_symlinks(filename_);
     slash = strrchr(filename, '/');
+
+#ifdef _WIN32
+    char *backslash = strrchr(filename, '\\');
+    if (backslash && (!slash || backslash > slash)) {
+        slash = backslash;
+    }
+#endif
+
     lockname = (slash
                 ? xasprintf("%.*s/.%s.~lock~",
                             (int) (slash - filename), filename, slash + 1)