ExternalData: Add support for multiple hash algorithms

Add support for projects to have `Data.txt.md5` *and* `Data.txt.sha512`
where the content links hold hashes for the same file.  Check all
`ExternalData_URL_TEMPLATES` entries in order for all available hashes.
The data acquisition is considered a failure if none of the available
URL resources has any of the given hashes.  This makes it possible to
have multiple data server resources where all servers do not support all
hashing algorithms.

Tests/Module/ExternalData/CMakeLists.txt

@@ -45,6 +45,8 @@ ExternalData_Add_Test(Data1
     -D Meta=DATA{MetaTop.dat,REGEX:Meta[ABC].dat}
     -D Directory=DATA{Directory/,A.dat,REGEX:[BC].dat}
     -D DirRecurse=DATA{DirRecurse/,RECURSE:,A.dat,REGEX:[BC].dat}
+    -D MultipleAlgorithmNoSHA1=DATA{MultipleAlgorithmNoSHA1.dat}
+    -D MultipleAlgorithmNoMD5=DATA{MultipleAlgorithmNoMD5.dat}
     -D "Semicolons=DATA{Data.dat}\\;DATA{Data.dat}"
     -P ${CMAKE_CURRENT_SOURCE_DIR}/Data1Check.cmake
   )

Tests/Module/ExternalData/MultipleAlgorithmNoMD5.dat.md5

@@ -0,0 +1 @@
+29848e54a4d0343f138ab14419b863de

Tests/Module/ExternalData/MultipleAlgorithmNoMD5.dat.sha1

@@ -0,0 +1 @@
+2af59a7022024974f3b8521b7ed8137c996a79f1

Tests/Module/ExternalData/MultipleAlgorithmNoSHA1.dat.md5

@@ -0,0 +1 @@
+08cfcf221f76ace7b906b312284e73d7

Tests/Module/ExternalData/MultipleAlgorithmNoSHA1.dat.sha1

@@ -0,0 +1 @@
+223b134e6e3a9bf34aa7531c009d97cff6b0d8a3