[uri] Escape the "+" character within HTTP form parameters

Within application/x-www-form-urlencoded values, a "+" character needs
to be escaped to avoid its being interpreted as a space.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/core/uri.c

diff --git a/src/core/uri.c b/src/core/uri.c
index ea0f2bc..824ad40 100644
--- a/src/core/uri.c
+++ b/src/core/uri.c
@@ -151,7 +151,7 @@
 	 */
 	static const char *escaped[URI_EPATH] = {
 		/* Scheme or default: escape everything */
-		[URI_SCHEME]	= "/#:@?=&",
+		[URI_SCHEME]	= "/#:@?=&+",
 		/* Opaque part: escape characters which would affect
 		 * the reparsing of the URI, allowing everything else
 		 * (e.g. ':', which will appear in iSCSI URIs).