export alpha channel (if present) when dumping to PGM format
export alpha channel (if present) when dumping to PGM format

Change-Id: Ica1818937fa03b29a749887d28f49fe675c8b1db

zofuthan/libwebp,ya7lelkom/libwebp,keane83/BLE_IM,jacklicn/libwebp,PKRoma/libwebp,altogother/webm.libwebp,gshORTON/webm.libwebp,appunite/libwebp,imazen/libwebp,kim42083/webm.libwebp,appunite/libwebp,ttyangf/libwebp,redengineer/libwebp,kleopatra999/webm.libwebp,ya7lelkom/libwebp,abwiz0086/webm.libwebp,Acidburn0zzz/webm.libwebp,redengineer/libwebp,Aexyn/libwebp,jiehu5114/libwebp,jiehu5114/libwebp,iniwf/webm.libwebp,ericmckean/webm.libwebp,jiehu5114/libwebp,imazen/libwebp,PKRoma/libwebp,cysp/libwebp,dumganhar/libwebp,abwiz0086/webm.libwebp,Suvarna1488/webm.libwebp,appunite/libwebp,zofuthan/libwebp,zofuthan/libwebp,Acidburn0zzz/webm.libwebp,comoyo/gonzo-libwebp,ya7lelkom/libwebp,comoyo/gonzo-libwebp,zofuthan/libwebp,redengineer/libwebp,cysp/libwebp,Tekserve/libwebp,Aexyn/libwebp,ttyangf/libwebp,ericmckean/webm.libwebp,matanbs/webm.libwebp,kim42083/webm.libwebp,PKRoma/libwebp,jiehu5114/libwebp,Distrotech/libwebp,ttyangf/libwebp,PKRoma/libwebp,comoyo/gonzo-libwebp,yohunl/libwebp,kalli123/webm.libwebp,Aexyn/libwebp,abwiz0086/webm.libwebp,ya7lelkom/libwebp,iniwf/webm.libwebp,imazen/libwebp,reimaginemedia/webm.libwebp,webmproject/libwebp,jiehu5114/libwebp,kalli123/webm.libwebp,ericmckean/webm.libwebp,ericmckean/webm.libwebp,keane83/BLE_IM,matanbs/webm.libwebp,kim42083/webm.libwebp,kalli123/webm.libwebp,reimaginemedia/webm.libwebp,Tekserve/libwebp,Maria1099/webm.libwebp,Tekserve/libwebp,rxl194/libwebp,iniwf/webm.libwebp,Acidburn0zzz/webm.libwebp,cysp/libwebp,appunite/libwebp,redengineer/libwebp,Aexyn/libwebp,webmproject/libwebp,Suvarna1488/webm.libwebp,altogother/webm.libwebp,comoyo/gonzo-libwebp,yohunl/libwebp,kim42083/webm.libwebp,webmproject/libwebp,keane83/BLE_IM,kim42083/webm.libwebp,comoyo/gonzo-libwebp,kleopatra999/webm.libwebp,Maria1099/webm.libwebp,webmproject/libwebp,altogother/webm.libwebp,imazen/libwebp,rxl194/libwebp,Maria1099/webm.libwebp,rxl194/libwebp,yohunl/libwebp,matanbs/webm.libwebp,reimaginemedia/webm.libwebp,jacklicn/libwebp,matanbs/webm.libwebp,altogother/webm.libwebp,Acidburn0zzz/webm.libwebp,appunite/libwebp,ttyangf/libwebp,gshORTON/webm.libwebp,comoyo/gonzo-libwebp,Aexyn/libwebp,abwiz0086/webm.libwebp,cysp/libwebp,ya7lelkom/libwebp,Suvarna1488/webm.libwebp,dumganhar/libwebp,keane83/BLE_IM,yohunl/libwebp,iniwf/webm.libwebp,Distrotech/libwebp,PKRoma/libwebp,kleopatra999/webm.libwebp,rxl194/libwebp,abwiz0086/webm.libwebp,gshORTON/webm.libwebp,Acidburn0zzz/webm.libwebp,yohunl/libwebp,kalli123/webm.libwebp,Suvarna1488/webm.libwebp,keane83/BLE_IM,kalli123/webm.libwebp,ttyangf/libwebp,PKRoma/libwebp,jacklicn/libwebp,dumganhar/libwebp,redengineer/libwebp,Maria1099/webm.libwebp,iniwf/webm.libwebp,Maria1099/webm.libwebp,zofuthan/libwebp,imazen/libwebp,ericmckean/webm.libwebp,gshORTON/webm.libwebp,reimaginemedia/webm.libwebp,Tekserve/libwebp,Distrotech/libwebp,kleopatra999/webm.libwebp,rxl194/libwebp,webmproject/libwebp,gshORTON/webm.libwebp,appunite/libwebp,jacklicn/libwebp,jacklicn/libwebp,altogother/webm.libwebp,matanbs/webm.libwebp,kleopatra999/webm.libwebp,Suvarna1488/webm.libwebp,comoyo/gonzo-libwebp,reimaginemedia/webm.libwebp