git: escape string values in configuration

This should handle the special characters that typically occur.

Fixes #1206

tests/modules/programs/git/git-expected.conf

@@ -1,6 +1,7 @@
 [alias]
-	a1 = foo
-	a2 = baz
+	a1 = "foo"
+	a2 = "baz"
+	escapes = "\"\\n\t"
 
 [commit]
 	gpgSign = true
@@ -10,33 +11,33 @@
 	integer = 38
 	multiple = 1
 	multiple = 2
-	name = value
+	name = "value"
 
 [extra "backcompat.with.dots"]
-	previously = worked
+	previously = "worked"
 
 [extra "subsection"]
-	value = test
+	value = "test"
 
 [filter "lfs"]
-	clean = git-lfs clean -- %f
-	process = git-lfs filter-process
+	clean = "git-lfs clean -- %f"
+	process = "git-lfs filter-process"
 	required = true
-	smudge = git-lfs smudge -- %f
+	smudge = "git-lfs smudge -- %f"
 
 [gpg]
-	program = path-to-gpg
+	program = "path-to-gpg"
 
 [user]
-	email = user@example.org
-	name = John Doe
-	signingKey = 00112233445566778899AABBCCDDEEFF
+	email = "user@example.org"
+	name = "John Doe"
+	signingKey = "00112233445566778899AABBCCDDEEFF"
 
 [include]
-	path = ~/path/to/config.inc
+	path = "~/path/to/config.inc"
 
 [includeIf "gitdir:~/src/dir"]
-	path = ~/path/to/conditional.inc
+	path = "~/path/to/conditional.inc"
 
 [includeIf "gitdir:~/src/dir"]
-	path = @git_include_path@
+	path = "@git_include_path@"