Verify pkg hash

[coatless]

Per Simon's e-mail on R-SIG-MAC, we're going to implement a check that verifies the md5 hash of the file.

Sample function:

#1 Path to File
#2 md5 Hash to Check Against
check_md5_hash() {
	
    # Obtain file hash
    FILE_HASH=$(md5 $1 | awk '{print $4}')
    
    # MD5 (path/to/file.pkg) = c29700c4e7b2914073ef7e741eb105bc
    #  1 %         2        %3%      4 
     
    # Check against hash
    if [ "$FILE_HASH" = "$2" ]; then
       echo 0
    else 
       exit 1
    fi
}

Hard coded hashes:

• clang-4.0.0-darwin15.6-Release.tar.gz: 2bec4fbae8d9caf6499c941ef9b87eae
  • Downloaded from: http://r.research.att.com/libs/clang-4.0.0-darwin15.6-Release.tar.gz
• gfortran (OS dependent)
  • gfortran-6.1-ElCapitan.dmg: 457b59a6453069cf72dee9a4f9bf1b0a
    • Downloaded from: http://coudert.name/software/gfortran-6.1-ElCapitan.dmg
  • gfortran-6.3-Sierra.dmg: 1849cea667bb714c5c04a8565a9fe231
    • Downloaded from: http://coudert.name/software/gfortran-6.3-Sierra.dmg