Darwin: allow calling make install more than once

This commit ensures that `gzip` does not overwrite any of the repo
files, because that prevents `make install` from executing more than
once.

.gitignore

@@ -260,6 +260,7 @@ docs/generated
 build/Makefile
 
 # debian stuff
+debian/i2pd.1.gz
 .pc/
 
 # qt 

Makefile.homebrew

@@ -44,7 +44,7 @@ install: all
 	install -m 644 contrib/i2pd.conf contrib/subscriptions.txt contrib/tunnels.conf ${PREFIX}/etc/i2pd
 	@cp -R contrib/certificates ${PREFIX}/share/i2pd/
 	install -m 644 ChangeLog LICENSE README.md contrib/i2pd.conf contrib/subscriptions.txt contrib/tunnels.conf ${PREFIX}/share/doc/i2pd
-	@gzip debian/i2pd.1 && install debian/i2pd.1.gz ${PREFIX}/share/man/man1
+	@gzip -kf debian/i2pd.1 && install debian/i2pd.1.gz ${PREFIX}/share/man/man1
 	@ln -sf ${PREFIX}/share/i2pd/certificates ${PREFIX}/var/lib/i2pd/
 	@ln -sf ${PREFIX}/etc/i2pd/i2pd.conf ${PREFIX}/var/lib/i2pd/i2pd.conf
 	@ln -sf ${PREFIX}/etc/i2pd/subscriptions.txt ${PREFIX}/var/lib/i2pd/subscriptions.txt