Fix bugs on make

[asmsuechan]

Hello!

I fixed some bugs on make for mac(unix).

PIX_FMT_BGR24 error

on make, this error occurred.

../../src/ardrone/video.cpp:81:61: error: use of undeclared identifier 'PIX_FMT_BGR24'; did you mean 'AV_PIX_FMT_BGR24'?
        bufferBGR = (uint8_t*)av_mallocz(avpicture_get_size(PIX_FMT_BGR24, pCodecCtx->width, pCodecCtx->height) * sizeof...
                                                            ^~~~~~~~~~~~~
                                                            AV_PIX_FMT_BGR24
../../src/ardrone/video.cpp:87:132: error: use of undeclared identifier 'PIX_FMT_BGR24'; did you mean 'AV_PIX_FMT_BGR24'?
  ...pCodecCtx->height, pCodecCtx->pix_fmt, pCodecCtx->width, pCodecCtx->height, PIX_FMT_BGR24, SWS_SPLINE, NULL, NULL, NULL);
                                                                                 ^~~~~~~~~~~~~
                                                                                 AV_PIX_FMT_BGR24
../../src/ardrone/video.cpp:103:61: error: use of undeclared identifier 'PIX_FMT_BGR24'; did you mean 'AV_PIX_FMT_BGR24'?
        bufferBGR = (uint8_t*)av_mallocz(avpicture_get_size(PIX_FMT_BGR24, pCodecCtx->width, pCodecCtx->height));
                                                            ^~~~~~~~~~~~~
                                                            AV_PIX_FMT_BGR24

Recent ffmpeg(>=3.0) doesn't declare PIX_FMT_BGR24, discussed in this issue.

library option error

on make, this error occurred.

g++ ../../src/ardrone/ardrone.o ../../src/ardrone/command.o ../../src/ardrone/config.o ../../src/ardrone/udp.o ../../src/ardrone/tcp.o ../../src/ardrone/navdata.o ../../src/ardrone/version.o ../../src/ardrone/video.o ../../src/main.o -o test.a -O2 -Wall -D__STDC_CONSTANT_MACROS   -lm -lpthread -lavutil -lavformat -lavcodec -lswscale -lopencv_calib3d -lopencv_core -lopencv_features2d -lopencv_flann -lopencv_highgui -lopencv_imgcodecs -lopencv_imgproc -lopencv_ml -lopencv_objdetect -lopencv_photo -lopencv_stitching -lopencv_superres -lopencv_video -lopencv_videoio -lopencv_videostab
ld: library not found for -lopencv_imgcodecs
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make: *** [test.a] Error 1

opencv_imgcodecs not found in opencv 2.4, discussed in this issue

env

$ sw_vers
ProductName:    Mac OS X
ProductVersion: 10.11.5
BuildVersion:   15F34
$  brew info opencv
homebrew/science/opencv: stable 2.4.13 (bottled), HEAD
Open source computer vision library
$ ffmpeg
ffmpeg version 3.0.2 Copyright (c) 2000-2016 the FFmpeg developers