add avconv support

src/app/avconv/avconv.patch

@@ -0,0 +1,21 @@
+- avoid compile error "‘for’ loop initial declarations are only
+  allowed in C99 or C11 mode"
+
++++ src/lib/libav/avconv.c
+@@ -426,6 +426,7 @@ static int alloc_buffer(InputStream *ist, FrameBuffer **pbuf)
+     int h_chroma_shift, v_chroma_shift;
+     int edge = 32; // XXX should be avcodec_get_edge_width(), but that fails on svq1
+     int w = s->width, h = s->height;
++    int i;
+ 
+     if (!buf)
+         return AVERROR(ENOMEM);
+@@ -449,7 +450,7 @@ static int alloc_buffer(InputStream *ist, FrameBuffer **pbuf)
+     memset(buf->base[0], 128, ret);
+ 
+     avcodec_get_chroma_sub_sample(s->pix_fmt, &h_chroma_shift, &v_chroma_shift);
+-    for (int i = 0; i < FF_ARRAY_ELEMS(buf->data); i++) {
++    for (i = 0; i < FF_ARRAY_ELEMS(buf->data); i++) {
+         const int h_shift = i==0 ? 0 : h_chroma_shift;
+         const int v_shift = i==0 ? 0 : v_chroma_shift;
+         if (s->flags & CODEC_FLAG_EMU_EDGE)

src/app/avconv/target.mk

@@ -0,0 +1,23 @@
+include $(REP_DIR)/lib/import/import-av.inc
+
+TARGET = avconv
+SRC_C  = avconv.c cmdutils.c avconv_opt.c avconv_filter.c
+LIBS  += avfilter avformat avcodec avutil avdevice swscale avresample
+LIBS  += base posix
+
+CC_WARN += -Wno-parentheses -Wno-switch -Wno-uninitialized \
+           -Wno-format-zero-length -Wno-pointer-sign
+
+LIBAV_PORT_DIR := $(call select_from_ports,libav)
+
+# version.h
+INC_DIR += $(PRG_DIR)
+
+# config.h
+INC_DIR += $(REP_DIR)/src/lib/libav
+
+CC_C_OPT += -DLIBAV_VERSION=\"0.8\"
+
+vpath %.c $(LIBAV_PORT_DIR)/src/lib/libav
+
+CC_CXX_WARN_STRICT =