cmake: Fix gettext pot update check.

When the feature was added in d93f6350, I did not adequately test for
the normal case when the pot is not updated.

This does not work because the pot has a timestamp in the
POT-Creation-Date: field.

Fix check-pot-update.cmake to ignore the pot timestamp and not report
the pot as changed when it has not been.

Signed-off-by: Rafael Kitover <rkitover@gmail.com>

src/wx/check-pot-updated.cmake

@@ -2,9 +2,22 @@ if(NOT EXISTS ${BIN_DIR}/wxvbam.pot)
     return()
 endif()
 
-file(READ ${SRC_DIR}/wxvbam.pot src_ver)
+macro(read_pot path var)
+    file(READ ${path} ${var}_file)
 
-file(READ ${BIN_DIR}/wxvbam.pot new_ver)
+    string(REGEX REPLACE ";"     "\\\\;" ${var}_file ${${var}_file})
+    string(REGEX REPLACE "\r?\n" ";"     ${var}_file ${${var}_file})
+
+    # Ignore timestamp.
+    foreach(line IN LISTS ${var}_file)
+        if(NOT line MATCHES [=[^"POT-Creation-Date: ]=])
+            list(APPEND ${var} ${line})
+        endif()
+    endforeach()
+endmacro()
+
+read_pot(${SRC_DIR}/wxvbam.pot src_ver)
+read_pot(${BIN_DIR}/wxvbam.pot new_ver)
 
 if(NOT src_ver STREQUAL new_ver)
     file(COPY ${BIN_DIR}/wxvbam.pot DESTINATION ${SRC_DIR})