Introduce environment variable UPX_DISABLE_GITREV_WARNING.

.github/travis_testsuite_1.sh

@@ -168,6 +168,7 @@ if [[ $BM_B =~ (^|\+)coverage($|\+) ]]; then
 fi
 
 export UPX="--prefer-ucl --no-color --no-progress"
+export UPX_DISABLE_GITREV_WARNING=1
 
 # let's go
 if ! $upx_run --version;          then echo "UPX-ERROR: FATAL: upx --version FAILED"; exit 1; fi

src/main.cpp

@@ -1540,11 +1540,18 @@ int __acc_cdecl_main main(int argc, char *argv[])
 
     if (gitrev[0])
     {
-        FILE *f = stdout;
+        bool warn = true;
-        int fg = con_fg(f,FG_RED);
+        const char *ee = getenv("UPX_DISABLE_GITREV_WARNING");
-        con_fprintf(f,"\nWARNING: this is an unstable beta version - use for testing only! Really.\n");
+        if (ee && ee[0] && strcmp(ee, "1") == 0)
-        fg = con_fg(f,fg);
+            warn = false;
-        UNUSED(fg);
+        if (warn)
+        {
+            FILE *f = stdout;
+            int fg = con_fg(f, FG_RED);
+            con_fprintf(f, "\nWARNING: this is an unstable beta version - use for testing only! Really.\n");
+            fg = con_fg(f, fg);
+            UNUSED(fg);
+        }
     }
 
 #if 0 && defined(__GLIBC__)