All 1990 entries now compile!

My first 41st, 51st and 29th (all depending on the base) birthday
updates (possibly more will follow but this is not a certainty). All the
1990 entries now compile!

In one we used a patch from Yusuke Endoh (thank you Yusuke!) which we
credited him in the README and in another we used a tip from him (use
-ansi at the compiler line) to get the other to compile (again, thank
you Yusuke!). We fixed the others. In the case of 1990/tbr/tbr.c the
author had supplied a shorter version and we fixed that one too.

Added 1990/.gitignore which has the built files of 1990 so that after
doing `cd 1990 ; make all' running `git status .' will not show any
untracked files.

1990/dg/README.md

@@ -18,16 +18,18 @@
 
 ## Judges' comments
 
-    Some C preprocessors get confused about single quotes in certain cases.
+    Some C preprocessors got confused about single quotes in certain cases.
     In particular, the following source line:
 
-       Cb12(ase(bco(acp(bi(acp(bcp(acp(bpl(aqu(bqu(A))))))))))))))))))))))))))))))
+       b12(ase(bco(acp(bi(acp(bcp(acp(bpl(aqu(bqu(A))))))))))))))))))))))))))))))
 
-    may need to be changed to:
+    sometimes has to be changed to:
 
-       Cb12(ase(bco(acp(bi(acp(bcp(acp(bpl('A'))))))))))))))))))))))))))))
+       b12(ase(bco(acp(bi(acp(bcp(acp(bpl('A'))))))))))))))))))))))))))))
+
+    if the C preprocessor botches single quotes in cpp expansions, which we have
+    done for the wider audience.
 
-    if your C preprocessor botches single quotes in cpp expansions.
 
 ## Author's comments