Remove the embedded sha1 code, and use one of botan or gcrypt

This adds a hard dependency on one of Botan or gcrypt. Botan is already a
recommended dependency, and gcrypt is probably packaged almost everywhere,
so this should not be a big deal.

ref #3241

louloulibs/cmake/Modules/FindGCRYPT.cmake

@@ -0,0 +1,35 @@
+# - Find gcrypt
+# Find the gcrypt cryptographic library
+#
+# This module defines the following variables:
+#   GCRYPT_FOUND  -  True if library and include directory are found
+# If set to TRUE, the following are also defined:
+#   GCRYPT_INCLUDE_DIRS  -  The directory where to find the header file
+#   GCRYPT_LIBRARIES  -  Where to find the library file
+#
+# For conveniance, these variables are also set. They have the same values
+# than the variables above.  The user can thus choose his/her prefered way
+# to write them.
+#   GCRYPT_LIBRARY
+#   GCRYPT_INCLUDE_DIR
+#
+# This file is in the public domain
+
+find_path(GCRYPT_INCLUDE_DIRS NAMES gcrypt.h
+  PATH_SUFFIXES gcrypt
+  DOC "The gcrypt include directory")
+
+find_library(GCRYPT_LIBRARIES NAMES gcrypt
+  DOC "The gcrypt library")
+
+# Use some standard module to handle the QUIETLY and REQUIRED arguments, and
+# set GCRYPT_FOUND to TRUE if these two variables are set.
+include(FindPackageHandleStandardArgs)
+find_package_handle_standard_args(GCRYPT REQUIRED_VARS GCRYPT_LIBRARIES GCRYPT_INCLUDE_DIRS)
+
+if(GCRYPT_FOUND)
+  set(GCRYPT_LIBRARY ${GCRYPT_LIBRARIES})
+  set(GCRYPT_INCLUDE_DIR ${GCRYPT_INCLUDE_DIRS})
+endif()
+
+mark_as_advanced(GCRYPT_INCLUDE_DIRS GCRYPT_LIBRARIES)